Engineering 
Library 


STEAM-ENGINE 
PRINCIPLES  AND  PRACTICE 

TERRELL  CROFT,  EDITOR 


CONTRIBUTORS 

The  following  have  contributed  manuscript  or  data  or 
have  otherwise  assisted  in  the  preparation  of  this  work : 

EDMUND  SIROKY 

H.  C.  CROFT         A.  J.  DIXON         E.  R.  POWELL 
Terrell  Croft  Engineering  Company 


BOOKS  BY 
TERRELL  CROFT 

PUBLISHED  BY 

McGRAW-HILL  BOOK  COMPANY,  INC. 


THE  AMERICAN  ELECTRICIAN'S  HANDBOOK, 
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STEAMI-ENGINE 
PRINCIPLES  AND  PRACTICE 


TERRELL  CROFT,  EDITOR 

M 

CONSULTING   ENGINEER.      DIRECTING   ENGINEER,   TERRELL   CROFT   ENGINEERING   CO. 

MEMBER   OP   THE   AMERICAN   SOCIETY   OP   MECHANICAL   ENGINEERS. 

MEMBER   OP   AMERICAN    INSTITUTE    OP    ELECTRICAL    ENGINEERS. 

MEMBER   OP   THE   ILLUMINATING   ENGINEERING   SOCIETY. 

MEMBER    AMERICAN    SOCIETY   TESTING   MATERIALS. 


FIRST  EDITION 
FIRST  IMPRESSION 


McGRAW-HILL  BOOK  COMPANY,  INC. 
NEW  YORK:  370  SEVENTH  AVENUE 

LONDON:  6  &  8  BOUVERIE  ST.,  E.  C.  4 
1922 


C7 

ngineeri 
library 


COPYRIGHT,  1922,  BY  TERRELL  CROFT 


THE   MAPLE   PKESS   VOKK  FA 


PREFACE 

STEAM-ENGINE  PRINCIPLES  AND  PRACTICE  has  been  very 
carefully  prepared  to  satisfy  what  is  thought  to  have  been  a 
long-felt  need  for  a  "practical"  book  which  would  contain 
the  information  that  an  operating  engineer  or  a  plant  super- 
intendent requires  concerning  steam  engines.  Although  there 
exists  a  popular  impression  that,  since  the  advent  of  the 
steam  turbine,  the  steam  engine  is  no  longer  of  any  conse- 
quence in  the  generation  of  mechanical  energy  (power),  noth- 
ing could  be  more  erroneous.  Under  certain  conditions,  the 
steam  engine  is  still — and  probably  always  will  be — a  very 
desirable  and  economical  prime  mover. 

No  attempt  has  been  made  to  include  in  this  book  anything 
which  pertains  to  the  design  of  steam  engines.  The  treatment 
has  been  directed  toward  what  may  be  termed  the  "use"  of 
the  engines.  That  is,  the  aim  has  been  to  supply  such  infor- 
mation as  will  enable  the  reader  to  wisely  select,  operate,  care 
for,  and  repair  steam  engines  and  to  make  a  study  of  and 
where  possible  to  improve  their  economy.  No  "higher 
mathematics"  is  employed;  a  working  knowledge  of  arith- 
metic should  enable  one  to  understand  all  which  is  presented. 

Drawings  for  all  of  the  548  illustrations  were  made  especially 
for  this  work.  It  has  been  the  endeavor  to  so  design  and 
render  these  pictures  that  they  will  convey  the  desired  infor- 
mation with  a  minimum  of  supplementary  discussion. 

Throughout  the  text,  principles  which  are  presented  are 
explained  with  descriptive  expositions  or  with  worked-out 
arithmetical  examples.  Also,  at  the  end  of  each  of  the  16 
divisions  there  are  questions  to  be  answered  and,  where 
justified,  problems  to  be  solved  by  the  reader.  These  ques- 
tions and  problems  are  based  on  the  text  matter  in  the  division 
just  preceding.  If  the  reader  can  answer  the  questions  and 
solve  the  problems,  he  then  must  be  conversant  with  the 
subject  matter  of  the  division.  Detail  solutions  to  all  of  the 
problems  are  printed  in  an  appendix  in  the  back  of  the  book. 

As  to  the  general  order  of  treatment : — First  the  function  and 
principle  of  the  steam  engine  are  considered.  These  are 

vii 


viii  PREFACE 

followed  by  a  division  on  nomenclature  and  classification. 
Next  follows  a  treatment  of  indicators  and  their  many  uses. 
Then  the  two  most  important  functioning  parts  of  the  engine — 
the  valves  and  the  governor — are  fully  treated  under  the  divi- 
sion titles  of:  slide  valves  and  their  adjustment,  Corliss  and 
poppet  valves  and  their  adjustment,  fly-ball  steam-engine 
governors,  and  shaft  steam-engine  governors. 

The  economics  of  the  use  of  condensers  with  steam  engines 
and  of  employing  multi-expansion  engines  are  next  considered 
and  are  followed  by  a  division  on  steam-engine  efficiencies  and 
how  to  increase  them.  The  material  in  the  next  division,  on 
steam  engines  of  modern  types,  concerns  the  distinctive 
features,  economics  and  costs  of  engines  of  the  present  day. 
The  testing  of  steam  engines  is  then  treated.  Following  this 
are  divisions  on  the  management,  operation  and  repair  of 
reciprocating  engines  and  on  the  use  of  superheated  steam  in 
engines  which,  it  is  hoped,  will  be  of  great  value  to  the  engineer. 

Next,  the  selection  of  steam  engines  is  discussed  from  a 
purely  but  broadly  economic  standpoint.  Finally,  a  thorough 
treatment  of  lubrication  is  presented  which,  although  it 
relates  specifically  to  steam  engines,  should  prove  of  general 
value  also  as  it  applies  to  other  machinery. 

With  this,  as  with  the  other  books  which  have  been  prepared 
by  the  editor,  it  is  the  sincere  desire  to  render  it  of  maximum 
usefulness  to  the  reader.  It  is  the  intention  to  improve  the 
book  each  time  it  is  revised  and  to  enlarge  it  as  conditions 
may  demand.  If  these  things  are  to  be  accomplished  most 
effectively,  it  is  essential  that  the  readers  cooperate  with  us. 
This  they  may  do  by  advising  the  editor  of  alterations  which 
they  feel  it  would  be  desirable  to  make.  Future  revisions 
and  additions  will,  insofar  as  is  feasible,  be  based  on  such 
suggestions  and  criticisms  from  the  readers. 

Although  the  proofs  have  been  read  and  checked  very 
carefully,  it  is  possible  that  some  undiscovered  errors  may 
remain.  Readers  will  confer  a  decided  favor  in  advising  the 
editor  of  any  such.  TERRELL  CROFT. 

UNIVERSITY  CITY, 

ST.  Louis,  Mo., 

July,  1922. 


ACKNOWLEDGMENTS 

The  editor  desires  to  acknowledge  the  assistance  which  has 
been  rendered  by  various  engine  manufacturers  of  the  United 
States.  Among  them  are  the:  Allis-Chalmers  Manufacturing 
Company;  Ames  Iron  Works;  Chuse  Engine  and  Manufacturing 
Company;  C.  &  G.  Cooper  Company;  Erie  Ball  Engine  Company; 
Erie  City  Iron  Works;  Fulton  Iron  Works;  Harrisburg  Foundry 
and  Machine  Works;  Nordberg  Manufacturing  Company; 
Ridgway  Dynamo  and  Engine  Company;  Vilter  Manufacturing 
Company. 

Furthermore,  certain  of  the  text  material  appeared  originally 
as  articles  in  certain  trade  and  technical  periodicals  among 
which  are :  National  Engineer,  Power,  Power  Plant  Engineering 
and  Southern  Engineer. 

Numerical  values  for  tables  and  graphs  have,  in  certain 
instances,  been  taken  from  engineering  textbooks  of  recog- 
nized high  standing.  In  such  cases  acknowledgment  is  made 
at  the  places  in  the  text  where  the  values  are  used. 

Special  acknowledgment  is  hereby  accorded  Edmond 
Siroky,  Head  Mechanical  Engineer  of  The  Terrell  Croft 
Engineering  Company,  who  has  been  responsible  for  the 
technical  accuracy  of  the  book. 

Other  acknowledgments  have  been  made  throughout  the 
book.  If  any  has  been  omitted,  it  has  been  through  oversight 
and,  if  brought  to  the  author's  attention,  it  will  be  incor- 
porated in  the  next  edition. 

TERRELL  CROFT. 


IX 


CONTENTS 

STEAM-ENGINE  PRINCIPLES  AND  PRACTICE 

BY 

TERRELL  CROFT 

PAGE 

FRONTISPIECE iv 

PREFACE vii 

ACKNOWLEDGMENTS ix 

LIST  OF  SYMBOLS xii 

DIVISION  1. — FUNCTION  AND  PRINCIPLE  OF  THE  STEAM  ENGINE.  1 
DIVISION  2. — STEAM-ENGINE  MECHANISMS  AND  NOMENCLATURE  19 
DIVISION  3. — STEAM-ENGINE  INDICATORS  AND  INDICATOR  PRACTICE  40 

DIVISION  4. — SLIDE  VALVES  AND  THEIR  SETTING  . 84 

DIVISION  5. — CORLISS  AND  POPPET  VALVES  AND  THEIR  SETTING  146 
DIVISION  6. — FLY-BALL  STEAM-ENGINE  GOVERNORS,  PRINCIPLES 

AND  ADJUSTMENT 192 

DIVISION  7. — SHAFT  STEAM-ENGINE  GOVERNORS,  PRINCIPLES  AND 

ADJUSTMENT 228 

DIVISION  8.— COMPOUND  AND  MULTI-EXPANSION  ENGINES  .  .  .  258 
DIVISION  9. — CONDENSING  AND  NON-CONDENSING  OPERATION.  .  283 
DIVISION  10. — STEAM-ENGINE  EFFICIENCIES  AND  How  TO  INCREASE 

THEM 291 

DIVISION  11. — STEAM  ENGINES  OF  MODERN  TYPES 319 

DIVISION  12. — STEAM-ENGINE  TESTING 342 

DIVISION  13. — RECIPROCATING-ENGINE  MANAGEMENT,  OPERATION, 

AND  REPAIR 373 

DIVISION  14. — USE  OF  SUPERHEATED  STEAM  IN  ENGINES  ....  417 

DIVISION  15. — SELECTING  AN  ENGINE 427 

DIVISION  16. — STEAM-ENGINE  LUBRICATION 447 

SOLUTIONS  TO  PROBLEMS 488 

INDEX  .  .  497 


XI 


STEAM  ENGINE  PRINCIPLES  AND  PRACTICE 
LIST  OP  SYMBOLS 

The  following  list  comprises  practically  all  of  the  symbols  which  are 
used  in  formulas  in  this  book.  Symbols  which  are  not  given  in  this 
list  are  defined  in  the  text  where  they  are  first  used.  When  any  symbol 
is  used  with  a  meaning  different  from  that  specified  below,  the  correct 
meaning  is  stated  in  the  text  where  the  symbol  occurs. 

SECTION 
SYMBOL  MEANING  FIRST  USED 

AiP  Area  of  piston,  exclusive  of  area  of  rod,  in  square  inches 17 

Cm  Mean  specific  heat  of  superheated  steam 317 

Dps  Density  of  steam,  in  pounds  per  cubic  foot 129 

di  Diameter,  in  inches 360 

E  Voltage  or  electromotive  force,  in  volts 361 

Ed  Efficiency,  expressed  decimally 362 

ErfTO  Mechanical  efficiency,  expressed  decimally 321 

E</(  Thermal  efficiency  of  ideal  Rankine  cycle,  expressed  decimally  .  315 

Edtb  Thermal  efficiency  based  on  brake  horse  power,   expressed 

decimally 322 

Edti  Thermal  efficiency  based  on  indicated  horse  power,  expressed 

decimally 317 

Fc  Centrifugal  force,  in  pounds 222 

Hd  Total  heat  of  dry  saturated  steam,  in  B.t.u.  per  pound 317 

HI  Heat  of  liquid,  in  B.t.u.  per  pound 315 

Ht  Total  heat  of  steam,  in  B.t.u.  per  pound 315 

7/t,  Latent  heat  of  vaporization,  in  B.t.u.  per  pound 317 

I  Current,  in  amperes 361 

K  A  constant 19 

k  Horse  power  constant 121 

kb  Brake  constant 380 

Lf  Effective  length  of  brake  arm,  in  feet 357 

LfS  Length  of  stroke,  in  feet 17 

Lhi  Height,  in  inches 224 

Mr  Regulation  coefficient,  expressed  decimally 219 

N  Angular  speed,  in  revolutions  per  minute 18 

Nf  Engine  speed  at  full  load,  in  revolutions  per  minute 219 

Nn  Engine  speed  at  no  load,  in  revolutions  per  minute 219 

N8  Number  of  double  strokes  per  minute 18 

TT  3.1416 ...  357 

Pa  Pressure,  in  pounds  per  square  inch  absolute 

Pg  Pressure,  in  pounds  per  square  inch  gage 19 

xii 


LIST  OF  SYMBOLS  xiii 

SECTION 

SYMBOL                                                      MEANING                                                        FIRST  USED 

Pm     Mean  effective  pressure,  in  pounds  per  square  inch 17 

P       Power  developed  in  one  end  of  a  cylinder,  in  foot  pounds  per 

minute 18 

PbhP   Brake  horse  power 321 

Php    Power,  in  horse  power 360 

PaP   Power  developed  in  one  end  of  a  cylinder,  in  horse  power 18 

PihV   Total  indicated  horse  power  of  an  engine. 321 

Pkw    Power,  in  kilowatts 361 

n       Radius,  in  inches 222 

Tf     Temperature,  in  degrees  Fahrenheit 371 

Tn      Superheat,  in  degrees  Fahrenheit 317 

th       Time,  in  hours 373 

ts        Time,  in  seconds 379 

Vi      Volume,  in  cubic  inches 379 

W      Work  done  in  one  end  of  a  cylinder  per  double  stroke,  in  foot 

pounds 17 

W      Weight,  in  pounds 222 

Wa    Weight  of  steam  used  in  one  end  of  a  cylinder  per  indicated 

horse  power  hour,  in  pounds 129 

W«     Weight  of  steam  used  per  horse  power  hour,  in  pounds 316 

W,b    Weight  of  steam  used  per  brake  horse  power  hour,  in  pounds .  322 

Wsd   Weight  of  dry  steam,  in  pounds 372 

W,«n,  Weight  of  dry  steam  per  brake  horse  power  hour,  in  pounds.  .  373 

Wsdi  Weight  of  dry  steam  per  indicated  horse  power  hour,  in  pounds .  373 

Wsi    Weight  of  steam  per  indicated  horse  power  hour,  in  pounds. . .  317 

Wsw  Weight  of  wet  steam,  in  pounds 372 

xc       Clearance  volume  expressed  as  a  fraction  of  piston  displacement  130 

Xd      Quality  of  steam,  expressed  decimally 317 

xp      Quality  of  steam,  in  per  cent 371 

xs       Fraction  of  stroke .  129 


STEAM  ENGINE 
PRINCIPLES  AND  PRACTICE 


DIVISION  1 

FUNCTION  AND  PRINCIPLE  OF  THE  STEAM 
ENGINE 

1.  The  Function  Of  The  Steam  Engine  is  to  convert  heat 
energy  into  mechanical  work.  The  heat  energy  is  evolved 
by  the  combustion  of  a  fuel  within  a  furnace  which  is  so 
arranged  that  the  heat  will  be  transferred  to  water  within  an 
adjacent  boiler.  The  water  is  thus  converted  into  steam  which 
is  then  conducted  to  the  engine.  Within  the  engine  the  steam 
is  compelled  to  do  mechanical  work  and,  in  so  doing,  loses  a 
portion  of  its  stock  of  heat  energy.  The  mechanical  work  is 
transmitted  from  the  engine  to  the  place  where  it  may  be 
useful  by  means  of  belts,  ropes,  chains,  or  other  connectors. 
Or,  it  may  be  converted  into  electrical  energy  and  transmitted 
through  wires. 

NOTE. — THE  HEAT-FLOW  IN  A  STEAM-ENGINE  PLANT  is  illustrated 
in  the  frontispiece.  Coal  is  burned  within  the  furnace  producing  a  large 
volume  of  hot  gases  (2,500  deg.  fahr.).  The  path  of  these  gases  is  so 
restricted  that  they  must  impinge  upon  the  surfaces  of  tubes  of  the  boiler. 
These  tubes  contain  water  which  is,  by  the  burning  coal,  maintained  at  a 
temperature  of  approximately  366  deg.  fahr.  Heat  flows  from  the  hot 
gases  to  the  water  within  the  tubes.  The  temperature  of  the  gases  is 
thus  reduced  so  rapidly  that  they  leave  the  boiler  at  about  520  deg.  fahr. 
The  heat,  which  is  given  to  the  water,  evaporates  it  into  steam  at  366 
deg.  fahr.  The  steam  flows  to  the  engine  through  pipes,  wherein  some 
heat  is  lost,  and  reaches  the  compound  engine  at  a  temperature  of  364 
deg.  fahr.  In  the  high-pressure  cylinder  the  steam  does  work,  loses  heat 
energy  and  then  leaves  the  cylinder  at  a  temperature  of  246  deg.  fahr. 
It  is  then  conducted  to  the  low-pressure  cylinder  where  it  again  does  work 
and  loses  heat.  It  is  finally  rejected  from  the  engine  at  a  temperature  of 
130  deg.  fahr.  What  is  then  done  with  the  steam  does  not  affect  the 

1 


1v 

2       .STEAM  E%GINE[PRINCIPLES  AND  PRACTICE    [DIV.  i 

operation  of  the  engine  but  rather  the  efficiency  of  the  plant  as  a  whole. 
The  efficiency  of  the  engine  in  performing  its  function  will  be  discussed 
in  Div.  10. 

2.  The  Construction  Of  The  Elementary  Steam  Engine 
can  be  understood  by  a  study  of  Fig.  1  (see  also  Div.  2). 
Essentially,  the  important  parts  of  the  engine  are  the  valve, 
V,  cylinder,  C,  piston,  P,  frame,  Fj  and  the  moving  parts 
whereby  the  motion  of  the  piston  is  transmitted  to  some  other 


Flywheel -•• 

Connecting  Rod—--. 

Cross  head-. 
Stuffing  Bo 
Piston  Rod- N 

Piston-.        \ 
Cylinder 


Crank-Shaft  Bearing 


Crank 

.Eccentric  Strap 
Eccentric 


!  Cylinder 
\  Head 
Cylinder 
Port  j:. 

Exhaust  Port'  ! 
Slide  Valve-^ 


Crank  Shaft''  : 
'Eccenfr/c  Pu/ley  • ' ' 
Rod 


^^Va/ve  Stem 

"—Inlet  For  Steam  From  Bofler 
-Steam  Chest 
" 'Steam  Outlet  (Exhaust) 

FIG.  1. — A  typical  simple  slide-valve  engine. 


machine  and  whereby  the  proper  motions  are  given  to  the 
valve.  The  valve  opens  passages  through  which  steam 
may  flow  into  the  cylinder  from  the  boiler  or  out  of  the  cylinder 
into  the  atmosphere.  (The  spent  or  exhaust  steam  may,  if 
desirable,  be  led,  instead  of  into  the  atmosphere,  into  a  con- 
denser or  into  a  heater.)  The  steam,  when  thus  admitted  into 
the  cylinder,  exerts  a  pressure  or  pushes  against  the  piston 
which  fits  closely  within  the  cylinder.  The  steam  is  thus 
capable  of  moving  the  piston  against  some  resistance — or,  in 
other  words,  the  steam  is  capable  of  doing  work  upon  the 
piston. 

3.  "Clearance"  Or  "Clearance  Volume"  are  terms  which 
should  be  understood  before  the  reader  proceeds.     Clearance 


SEC.  4] 


PRINCIPLE  OF  THE  STEAM  ENGINE 


applies  to  the  space  between  the  piston  and  the  end  of  the 
cylinder,  together  with  the  steam  passages  as  far  as  the  valves, 
when  the  piston  is  at  one  extreme  end  of  its  travel.  Since  it 
is  mechanically  unsafe  to  attempt  the  construction  of  an 
engine  without  some  clearance,  all  actual  engines  are  built 
with  a  certain  amount  of  clearance.  Only  engines  with 
clearance  will  be  considered  in  this  book.  Clearance  is 
usually  expressed  as  a  percentage  of  the  volume  (displacement 
volume)  through  which  the  piston  sweeps.  The  displacement 
volume  =  area  of  piston  X  length  of  stroke. 

EXAMPLE. — An  18  in.  by  30  in.  engine  (Fig.  2)  has  clearance  volumes 
of  (1)  head  end — 141.3  cu.  in.  (2)  crank  end — 139.  cu.  in.  If  the  piston 
rod  is  2  in.  in  diameter  what  are  the 
clearances  in  per  cent,  of  displacement 
volume?  SOLUTION. — The  head-end 
displacement  volume  =  (18  X  18  X 
0.785)  X  30  =  7620  cu.  in.  The 
crank-end  displacement  volume  =  7620 
-  (2  X  2  X  0.785  X  30)  =  7526 
cu.  in.  Thus,  the  head-end  clearance 
~  141.3  -r-  7620  =  0.0186  or  1.86  per 
cent  Also,  the  crank-end  clearance 
=  139  -r-  7526  =  0.0185  or  1.85  per 
cent. 

NOTE. —  "PISTON  CLEARANCE"  OR  "LINEAL  CLEARANCE"  refers  only 
to  the  distance  between  the  piston  and  the  end  of  the  cylinder  (the 
cylinder  head)  when  the  piston  is  at  that  end  of  its  travel.  Piston  clear- 
ance is  measured  in  linear  inches. 


Head-End  Clearance 
;' Vo/ume*  141.3  Cu. In. 


Crank-End  Clearance  •' 
Vo/utne  =  139  Cu  In.' 


FIG.  2. — What    are    the   clearances  in 
percentages  of  piston  displacement? 


4.  The  Operation  Of  The  Elementary  Steam  Engine  (Figs. 

3  and  4)  can  thus  be  explained: 


EXPLANATION. — Consider  an  engine  (Fig.  3)  which  is  equipped  with 
two  hand-operated  valves  V\  and  F2.  When  the  valve  levers  are  held 
in  the  position  shown  in  Fig.  3,  valve  Vz  will  permit  steam  to  flow  into 
the  cylinder  at  the  right-hand  side  of  the  piston.  Valve  Vi,  however,  is 
in  such  position  as  to  allow  the  escape  of  whatever  steam  or  air  may  be  at 
the  left-hand  side  of  the  piston.  Therefore,  the  pressure  of  the  steam 
acting  on  the  piston  will  force  the  piston  to  the  left.  After  the  piston  has 
traveled  as  far  as  the  connecting  rod  and  shaft  will  permit,  the  operator 
shifts  the  levers  to  the  positions  of  Fig.  4.  This,  since  it  permits  steam 
to  flow  into  the  cylinder  through  V\  and  out  through  F2,  will  reverse 
the  force  on  the  piston  and  drive  it  to  the  right.  If  the  valves  are  shifted 


4         STEAM  ENGINE  PRINCIPLES  AND  PRACTICE      [Div.  1 

Steam  From       Steam  From 
Boiler^  Engine,  (Exhaust) 


FIG.  3. — Section  through  cylinder  of  engine  with  hand-operated  valves. 


Sfeam  from        Steam  From 
Bo//er;  Engine,  (Exhaust) 


Flywheel^ 


FIG.  4. — Section  through  cylinder  of  engine  with  hand-operated  valves.  (This  is 
the  same  engine  as  shown  in  Fig.  3  but  with  the  valves  so  shifted  as  to  cause  the  piston 
to  move  in  the  opposite  direction.) 

Steam  From        Steam  From 
Boiler-..  Engine,  (Exhaust) 


FIG.  5. — Section  through  cylinder  of  engine  with  automatic  valves.  (This  shows 
how  the  valves  of  the  engine  of  Fig.  4  can  be  automatically  operated  from  the 
shaft.) 


SEC.  5] 


PRINCIPLE  OF  THE  STEAM  ENGINE 


by  the  operator  every  time  the  piston  reaches  one  end  of  its  path,  the 
steam  will  turn  the  shaft,  S,  continually. 

The  operation  of  the  valves,  V\  and  V2,  of  Figs.  3  and  4  can  be  made 
automatic  by  the  suggested  arrangement  of  Fig.  5  where  a  small  crank 
C,  on  the  shaft  is  employed  to  shift  the  valves.  Although  this  arrange- 
ment could  be  made  to  provide  regular  operation,  the  valves  and  their 
operating  mechanism  would  soon  show  a  wearing  down  at  the  nibbing 
surfaces  which  might  cause  leakage  past  the  valves  and  noisy  operation. 
To  provide  against  these  troubles,  a  simpler  mechanism  (Figs.  1  and  6) 
has  been  devised  wherein  but  one  valve  is  used  and  adjustment  for  wear 
(as  will  be  explained)  is  automatic. 


Steam 


..-Steam  From 

Boiler ^   .  VatveStem         Valve-Operating 
Crank- -^ 

.-Flywheel 


•Shaft 


FIG.  6. — Section  through  cylinder  of  an  engine  which  has  a  slide  valve. 

5.  Heat  Is  Energy  (as  explained  in  the  author's  PRACTICAL 
HEAT).     Although  about  seven  existing  forms  of  energy  are 
known  but  two  of  these,  mechanical  and  electrical,  are  directly 
useful  for  power  purposes.     Now,  except  for  a  small  quantity 
of  mechanical  energy,  known  as  water  power,  nearly  all  of 
our  useful  energy  is  derived  from  chemical  energy  existent  in 
fuels.     By  combustion,  the  chemical  energy  of  the  fuels  can 
be  converted  into  heat  energy.     The  heat  energy  is  then 
(Sec.  1)  available  for  conversion  into  mechanical  energy. 

NOTE. — THE  HEAT  UNIT  HAS  EXACT  EQUIVALENTS  OF  MECHANICAL 
AND  ELECTRICAL  ENERGY.  Experiments  have  proved  that,  when  heat 
energy  is  converted  into  any  other  form  of  energy  or  when  any  form  of 
energy  is  converted  into  heat,  an  exact  and  definite  relationship  always 
exists.  Thus,  1  B.t.u.  (British  thermal  unit)  =  778  ft.  Ib.  =  ^545  h.p. 
hr.  =  0.000393  h.p.  hr.  =  ^41 5  kw.  hr.  =  0.000293  kw.  hr. 

6.  No  Heat  Engine  Can  Convert  Into  Work  All  Of  The  Heat 
Which  It  Receives.     The  heat  energy  which  the  working 
substance  (usually  steam)  contains  is  converted  into  work  by 
virtue  of  the  expansion  of  the  working  substance.     Now,  all 


6         STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  1 

of  the  heat  would  be  converted  into  work  only  after  the  sub- 
stance had  expanded  to  such  a  volume  that  its  temperature 
would  have  been  lowered  to  the  absolute  zero.  Furthermore, 
since  absolute  zero  is  a  temperature  which  will  probably  never 
be  attained,  and  surely  not  in  any  practical  machine,  it 
follows  that  no  substance  can  give  up  all  of  its  heat.  There- 
fore, if  used  in  a  heat  engine,  the  substance  cannot  convert 
into  work  all  of  the  heat  which  it  contains.  In  practice,  the 
heat  which  remains  in  the  working  substance,  after  the 
substance  has  reached  the  limit  of  its  expansion,  is  allowed 
to  remain  in  the  substance  —  that  is,  no  effort  is  made  to  con- 
vert this  remaining  heat  energy  into  work.  It  is,  therefore, 
heat  energy  which  is  rejected  (R,  Fig.  8),  or  not  abstracted  by 
the  engine.  Thus  the  energy  in  a  steam  engine's  exhaust 
represents  rejected  heat. 

7.  The  Ratio  Of  The  "Heat  Abstracted  "  By  An  Engine  To 
The  "Heat  Which  It  Receives"  May  Be  Called  Its  "Theoreti- 
cal Efficiency."  The  theoretical  efficiency  of  any  heat  engine 
is  fixed  by  the  specific  processes  whereby  the  working 
substance  does  work  in  the  cylinder  of  that  engine.  This 
theoretical  efficiency  cannot  be  exceeded  —  except,  sometimes, 
by  employing  different  processes.  The  theoretical  efficiency 
may  be  expressed  by  the  formula: 

Heat  abstracted         ,,     .      ,. 
(1)  Theoretical  efficiency  =  -  (decimal) 


EXAMPLE.  —  A  heat  engine  receives  100,000  B.t.u.  per  hour  from  a 

source  of  heat.     It  rejects  75,000  B.t.u.  per  hour.     What  is  its  theoretical 

efficiency?     SOLUTION.  —  By     For.     (1):  Theoretical      efficiency   =  Heat 

abstracted  /Heat  received  =  (Heat  received  —  Heat  rejected)  /Heat  received 

=  (100,000  -  75,000)  -J-  100,000  =  0.25  or  25  per  cent. 

8.  The  Most  Perfect  Steam  Engine  that  could  be  con- 
structed (Fig.  7)  would  have  to  fulfill  the  following  conditions: 
(1)  The  piston  and  cylinders  to  be  of  a  non-heat-conducting 
material.  (2)  Steam  to  be  admitted  at  a  constant  pressure  while 
the  piston  travels  outward  from  the  cylinder-end;  the  admission 
to  stop  at  such  instant  that,  (3)  The  steam  within  the  cylinder 
would  just  expand  —  adiabatically  —  to  the  pressure  at  which  it 
is  to  be  exhausted.  (4)  The  steam  to  be  exhausted  from  the 


SEC.  9] 


PRINCIPLE  OF  THE  STEAM  ENGINE 


cylinder  as  the  piston  travels  toward  the  cylinder-end;  the  exhaust 
to  cease  at  such  an  instant  that,  (5)  The  steam  remaining  within 
the  cylinder  would  be  compressed — adiabatically — so  as  to  just 
fill  the  clearance  space  at  exactly  the  pressure  of  the  steam  which 
is  about  to  be  admitted,  as  in  condition  (2).  Conditions  (2) 
to  (5)  above,  describe  the  cycle  or  processes  which,  when 
performed  with  a  non-heat- 
conducting  cylinder  and  pis- 
ton, would  give  the  highest 
theoretical  efficiency  possible 
for  any  steam  engine  work- 
ing between  certain  pressure 
limits.  All  steam-engine  steam 
efficiencies  are,  therefore,  re-  /n/ef'- 
ferred  to  the  efficiency  of  this 
engine  as  the  ideal  (Div.  10). 
The  processes  (cycle)  em- 
ployed by  such  an  ideal 
engine  are  called  the  ideal 

ClJCle. 


I-  Pressure  Diagram 


CUflet 


\  k- --Stroke- M 

'Non-Heat-Conducting  Piston 
^Non-Heat-Conducting  Cylinder 
H- Section  Through   Cylinder 

FIG.  7. — An  ideal  steam  engine.     (This 

-.  ,-..  —        .         — .  engine    operates    upon    the  ideal  Rankine 

9.    Any  Steam  Engine  Does     cycle  and  has>  therefore,  the  greatest  theo- 
ItS    Work    By    Virtue    Of    En-     retical  efficiency  that  any  engine  can  attain 

ergy  Which  It  Abstracts  From  when  working  between the pressures shown'; 
The  Steam;  see  A,  Fig.  8.  That  this  is  true  is  shown  by 
every  steam-engine  test.  It  was  shown  in  Sec.  1  for  the  engine 
illustrated  in  the  frontispiece,  that  the  steam  was  cooled  in 
passing  through  the  engine  from  364  deg.  fahr.  to  130  deg.  fahr. 
Furthermore,  a  test  would  have  shown  that  the  quality  of 
the  steam  was  also  decreased  in  passing  through  the  engine. 
The  loss  in  heat,  which  the  steam  undergoes  due  to  the 
lowering  of  its  temperature  and  the  decreasing  of  its  quality, 
represents  heat  abstracted  from  the  steam.  As  will  be  ex- 
plained, all  or  part  of  this  heat  loss  may  have  been  the  result 
of  the  conversion  of  heat  energy  into  mechanical  energy  (or 
work). 

EXAMPLE. — If,  in  the  plant  illustrated  in  the  frontispiece,  the  quality 
of  the  steam  entering  the  engine  is  99  per  cent,  and  that  of  the  leaving 
(exhaust)  steam  is  80  per  cent.,  how  much  heat  energy  is  abstracted 
from  each  pound  of  steam  that  the  engine  uses?  SOLUTION. — From 


8         STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.   1 

steam  tables  and  charts,  the  total  heat  of  1  Ib.  of  steam  at  364  deg.  fahr. 
and  of  99  per  cent,  quality  is  1186  B.t.u.  Likewise,  the  total  heat  of  1  Ib. 
of  steam  at  130  deg.  fahr.  and  of  80  per  cent,  quality  is  913  B.t.u. 
Therefore,  for  this  engine  the  heat  abstracted  =  1186  -  913  =  273 
B.t.u.  per  pound. 

10.  The  Ratio  Of  The  Work  Done  By  The  Steam  To  The 
Heat  Abstracted  From  The  Steam  depends  on  how  much  heat 
is  wasted  (L,  Fig.  8)  within  the  engine  cylinder.     If  an  engine 
could  be  constructed  with  non-heat-conducting  cylinder  and 
piston  it  would  be  possible  to  convert  into  work  all  of  the  heat 
which  is  abstracted  from  the  steam.     But,  since  no  non-heat- 
conducting  material   has  ever  been  discovered,  much  less  a 
heat  non-conductor  which  could  be  used  for  cylinder  and  piston 
construction,  the  steam  within  an  engine  cylinder  will  always 
lose  heat  (waste  it)  through  the  walls  and  the  piston.     This 
heat  which  is  lost  from  the  steam  within  the  cylinder  is  called 
a  thermal  loss. 

11.  The  "Total  Work  Done  By  The  Steam"  Constitutes 
Useful  Work  And  Mechanical  Losses ;   U  and  MI,  Fig.  8. 
The  work  done  by  the  steam  can  be  computed  (Sec.  17)  from 
the  pressures  which  it  exerts  upon  the  piston  and  the  distance 
it  causes  the  piston  to  move.     As  will  be  shown  in  Div.  3,  this 
work  can  be  measured.     If,  now,  all  of  the  engine's  moving 
parts  were  f rictionless,  all  of  the  work  done  by  the  steam 
would   then   be   available   for   transmission,    as   mechanical 
energy,  to  some  other  machine.     But,  since  friction  cannot 
be  entirely  eliminated  in  any  engine  mechanism  (Div.  16), 
it  follows  that  a  portion  of  the  work  done  by  the  steam  will 
be  used  up  or  lost  within  the  engine  itself  in  overcoming  the 
friction  of  its  own  parts.     This  portion  of  the  work  constitutes 
a  loss  and  may  be  termed  the  mechanical  loss — or  losses. 
Evidently,  only  that  energy  which  remains  after  the  friction 
is  overcome  can  be  utilized  as  mechanical  energy.     It  follows, 
therefore,  that: 

(2)  Work    done    by    steam  =  Mechanical    losses  +  Useful 
energy. 

12.  There  Is  A  Heat  Balance  For  Every  Steam  Engine; 

see  Fig.  8.     The  meaning  of  this  is  that  the  total  energy  leav- 


SEC.  13]          PRINCIPLE  OF  THE  STEAM  ENGINE 


ing  the  engine  in  various  forms  is  equal  to  the  total  heat  energy 
which  the  engine  receives.  The  various  ways  in  which  energy 
leaves  a  steam  engine  have  been  discussed  in  preceding  sec- 
tions and  may  be  summarized  as  follows  and  as  shown  in  Fig. 
8 :  Of  the  heat,  H,  which  an  engine  receives  only  a  small  part, 
A,  is  abstracted  whereas  the  greater  part,  R,  is  rejected  (Sec.  6). 
The  rejected  heat  is  not  useful  for  work  but  may  be  utilized 
for  building-heating  or  other  industrial  services.  The  heat, 
A,  which  the  engine  abstracts  may  be  divided  into:  (1)  That, 
T,  which  is  converted  into  work.  (2)  That,  L,  which  constitutes 
thermal  losses.  The  heat,  T,  may  again  be  separated  into: 
(1)  Useful  work,  U.  (2)  Mechanical  losses,  M,  Sec.  11. 


Heat  Flowing 
To  Engine^ 


Abstracted 
Heaf-,. 


.Total  Work 


Useful 


\  Done  By  Steam        Work  -. 


777/5  Heat  May  Be 
Employed,  But  Cannot, 
Be  Returned  To  The  Engine 


•Wasted  Heat 
\IO% 
FIG.  8. — An  elementary  heat  balance  for  a  typical  high-grade  steam  engine. 


NOTE. — AN  EFFICIENT  STEAM  ENGINE  is  one  in  which  the  ratio  of 
useful  work  to  heat  received  is  large.  An  efficient  power  plant  is  one  in 
which  such  use  is  made  of  the  rejected  heat,  R  (Fig.  8)  that  the  portion 
thereof  which  is  wasted  is  a  minimum. 

EXAMPLE. — For  the  engine,  the  heat  balance  of  which  is  shown  in 
Fig.  8,  H  represents  all  (100  per  cent.)  of  the  heat  added  to  the  water  in 
the  boiler  to  convert  the  water  into  steam.  Upon  receiving  the  steam, 
the  engine  abstracts  26  per  cent,  of  this  heat  and  rejects  the  remaining 
74  per  cent.  Within  the  cylinder,  8  per  cent,  of  the  original  100  are 
lost  thermally,  L,  while  18  per  cent,  is  converted  into  work,  T.  Of  this 
18  per  cent.,  2  per  cent,  is  lost  in  overcoming  mechanical  friction  and  the 
remaining  16  per  cent,  of  the  original  100  appears  as  useful  work.  That 
is,  for  this  engine,  as  explained  in  Sec.  7,  the  theoretical  efficiency  =  heat 
abstracted/  heat  received  =  26  -5-  100  =  0.26  =  26  per  cent. 

13.  How  Steam  Does  Work  By  Direct  Pressure  may  be 

understood  by  a  study  of  Fig.  9  (see  also  the  author's  PRAC- 
TICAL HEAT).  If,  with  the  piston  in  the  position  illustrated, 
valve  Vi  is  opened,  steam  will  be  admitted  into  the  space  to 


10       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  1 


the  left  of  the  piston.  It  will  exert  against  every  square  inch 
of  the  piston's  face  a  pressure  equal  to  that  at  which  the  steam 
is  generated  in  the  boiler.  This  pressure  will  exert  a  force 
tending  to  push  the  piston  to  the  right.  At  the  same  time, 
however,  the  air  acting  on  the  right-hand  face  of  the  piston  is 
exerting  against  every  square  inch  thereof  a  pressure  equal  to 
that  of  the  atmosphere.  It  is  evident  that  if  the  boiler-pres- 
sure exceeds  the  atmospheric  pressure,  there  will  be  an  unbal- 
anced force  on  the  piston 
tending  to  move  it  to  the 
right.  If  this  force  is  capable 
of  moving  the  piston,  work 
will  be  done  upon  the  piston. 

EXAMPLE. — If  the  boiler  pressure 
(Fig.  9)  is  100  Ib.  per  sq.  in.  abs.  and 
the  atmospheric  pressure  is  1.5  Ib. 
per  sq.  in.  abs.,  and  if  the  piston's 
area  is  100  sq.  in.,  the  total  force 
which  acts  on  the  left  face  of  the 
piston  will  be  100  sq.  in.  X  100  Ib. 
per  sq.  in.  =  10,000  Ib.  Likewise, 
the  force  acting  on  the  piston's 
right  face  will  be  100  sq.  in.  X  15 
Ib.  per  sq.  in.  =  1,500  Ib.  The  net  or  unbalanced  force  will  be  10,000  — 
1,500  =  8,500  Ib.  If,  now,  this  force  is  able  to  move  the  piston,  the 
work  done  for  each  foot  that  the  piston  is  moved  will  be  1  ft.  X  8,500 
Ib.  =  8,500  ft.  Ib.  If  the  stroke  (distance  moved  by  the  piston)  is  2 
ft.,  then  the  work  done  per  stroke  will  be  8,500  X  2  =  1 7,000  ft.  Ib. 

NOTE. — THE  "NET  PRESSURE"  ON  THE  PISTON,  at  any  instant,  is 
the  difference  between  the  pressures  on  its  two  sides.  The  work  done 
during  a  stroke  is  equal  to  the  product  of  the  average  net  pressure,  the 
piston's  area  and  the  length  of  the  stroke.  In  the  above  example  the 
net  pressure  is  100  —  15  =  85  Ib.  per  sq.  in. 

14.  Work  Must  Sometimes  Be  Done  Upon  The  Steam  In 
Expelling  It  From  The  Cylinder. — If,  in  Fig.  9,  after  the  piston 
reaches  the  position,  M ,  shown  by  dotted  lines,  Vi  is  closed 
and  F2  is  opened,  the  pressure  at  the  left  of  the  piston  will  be 
reduced  as  the  steam  escapes  through  V2  until  the  pressure 
in  the  cylinder  is  equal  to  that  within  the  vessel  into  which 
the  steam  exhausts.  This  pressure  is  called  the  back  pressure. 
The  value  of  this  back  pressure  may  vary  from  1  or  2  Ib.  per 


< -Stroke - 

I-Seciion  Through  Cylinder 

FIG.  9. — Work  diagram  for  an  engine  which 
takes  steam  for  a  full  stroke. 


SEC.  14]          PRINCIPLE  OF  THE  STEAM  ENGINE  11 

sq.  in.  abs.  (when  a  condenser  is  used,  Div.  9)  to  35  Ib.  per 
sq.  in.  abs.  or  more.  Whenever  the  back  pressure  is  in  excess 
of  atmospheric  pressure  (in  a  single-acting  engine  as  shown  in 
Fig.  9,)  the  net  pressure  on  the  piston  will  act  opposite  to  the 
direction  in  which  the  piston  must  be  moved  to  exhaust  the 
steam  from  the  cylinder.  Under  such  circumstances  this 
net  pressure  must  be  overcome  by  using  some  external  means 
for  exhausting  the  steam.  The  external  force  then  does  work 
upon  the  steam  in  overcoming  the  net  pressure.  As  in  the 
preceding  section,  the  work  done  is  equal  to  the  net  pressure 
times  the  piston  area  times  the  distance  moved  or  stroke. 

EXAMPLE. — If,  in  Fig.  9,  the  back  pressure  on  the  engine  is  20  Ib.  per 
sq.  in.  abs,  what  work  must  be  done  upon  the  steam  to  exhaust  it  and 
what  is  the  net  work  done  by  the  steam  per  double-stroke?  SOLUTION. — 
The  work  done  on  the  steam  during  each  exhaust  stroke  is  (20  —  15)  X 
100  X  2  =  1,000  ft.  Ib.  Since,  by  the  example  of  Sec.  13,  the  work  done 
during  the  admission  stroke  is  17,000  ft.  Ib.,  the  net  work  for  the  two 
strokes  is  17,000  -  1,000  =  16,000  ft.  Ib. 

NOTE. — THE  "EFFECTIVE  PRESSURE"  ON  AN  ENGINE  PISTON,  for 
any  of  its  positions,  is  the  difference  between  the  two  net  pressures 
which  act  upon  it  when  it  is  travelling  in  opposite  directions  through  that 
position.  Thus,  for  the  engine  of  Fig.  9,  the  effective  pressure  for  any 
position  is  85  —  5  =  80  Ib.  per  sq.  in.  The  net  work  of  the  steam  upon 
the  piston  could  have  been  found  by  multiplying  together  the  piston  area, 
stroke,  and  effective  pressure.  Thus:  net  work  =  100  X  2  X  80  = 
16,000  A  Ib. 

NOTE. — THE  "WORKING  STROKE"  OR  "POWER  STROKE"  of  any  heat 
engine  is  understood  to  mean  the  movement  of  the  piston  from  one  end 
of  its  travel  to  the  other  while  one  charge  of  the  working  substance  urges 
the  piston  onward.  Thus,  in  the  engine  of  Fig.  9,  the  movement  of  the 
piston  toward  the  right  constitutes  a  working  stroke.  The  return  of 
the  piston  to  the  left  is  termed  its  return  stroke.  A  working  stroke 
together  with  a  return  stroke  constitutes  a  double  stroke.  In  formulas  in 
this  book,  Na  =  number  of  working  strokes  per  minute. 

NOTE. — SINGLE  AND  DOUBLE-ACTING  ENGINES  are  those  in  which 
working  strokes  are  performed  as  the  piston  moves  respectively  in  one  or 
both  directions.  The  engine  of  Fig.  9,  since  steam  is  admitted  only  on 
one  side  of  its  piston,  is  a  single-acting  engine.  Steam  engines  are 
usually  constructed  so  as  to  admit  steam  to  both  sides  of  the  piston  (Fig. 
3) ;  they  are  then  double-acting  since  working  strokes  are  then  performed 
as  the  piston  moves  in  either  direction.  From  these  definitions  it  follows 
that  in  double-acting  steam  engines  each  stroke  is  a  working  stroke, 
whereas  in  single-acting  steam  engines  only  alternate  strokes  are  working 
strokes. 


12       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  1 


15.  How  Steam  Does  Work  By  Expansion  may  be  under- 
stood by  reference  to  Fig.  10.  The  same  engine  as  illustrated 
in  Fig.  9  is  now  shown  taking  steam  for  only  one-half  stroke. 
The  line  AB  represents  the  pressure  during  the  first  half- 
stroke  while  Vi  is  open.  When  Vi  is  closed  (B),  the  net 
pressure  of  the  steam  is  still  85  Ib.  per  sq.  in.  Further  move- 
ment of  the  piston  to  the  right,  however,  will  cause  the  pressure 
within  the  cylinder  to  decrease.  Thus,  as  the  piston  completes 
its  stroke,  the  pressure  will  drop  as  indicated  by  the  curve 

BC.     The  net  pressure  on  the 

Steam  Admitted;    Steam  Expanding -.  .    .  ,.,          .  , 

|   VtOpen.         Both  va/^s  closed    piston   likewise   decreases. 

Thus,  at  the  end  of  the  stroke, 
the  net  pressure  is  as  repre- 
sented by  GC.  The  back 
pressure  is  represented  by  EF 
or  by  GD.  Just  as  the  net 
pressure  varies  from  B  to  C, 
so  does  the  effective  pres- 
sure now  vary  for  different 
positions  from  B  to  C. 
Effective  pressures  are  now 
represented  by  the  vertical 


.„£- 

Steam 
Outlet 


-Stroke H 

31- Section  Through  Cylinder 

FIG.  10. — Work  diagram   for  an  engine 

which    takes   steam   for   only  part  stroke,  distances    trom    HiD  tO 

(This  engine  is  taking  steam  for  only  one-  ^IsO,     the    net    WOrk  is 

half  stroke.)  ,  _     _ 

sented    by   the   shaded  area 

ABODE.  The  net  work  is  computed  by  multiplying  together 
the  piston  area,  stroke,  and  average  or  mean  effective  pressure. 
Methods  of  finding  the  mean  effective  pressure  are  given  in 
Div.  3. 

EXAMPLE. — For  the  engine  of  Fig.  10,  the  mean  effective  pressure  is 
68  Ib.  per  sq.  in.  Therefore,  the  net  work  =  100  X  2  X  68  =  13,600 
ft.  Ib.  Of  this,  100  X  1  X  80  =  8,000  ft.  Ib.  were  done  along  AB  and 
13,600  -  8,000  =  5,600  ft.  Ib.  were  done  along  BC. 

16.  The  Economy  Of  Using  Steam  Expansively  is  illustrated 
by  the  example  of  the  preceding  section.  It  should  be  noted 
that,  in  Fig.  10,  since  steam  was  admitted  to  the  cylinder  for 
only  one-half  stroke,  the  weight  of  steam  admitted  was  little 
more  than  one-half  that  admitted  to  the  engine  of  Fig.  9.  As 
used  in  Fig.  9,  the  weight  of  steam  admitted  in  Fig.  10  would 


SEC.  17]          PRINCIPLE  OF  THE  STEAM  ENGINE  13 

do  only  about  8,000  ft.  Ib.  of  work.  But  in  Fig.  10  it  was 
found  to  do  13,600  ft.  Ib.  Now,  the  difference  of  5,600  ft. 
Ib.  was  done  at  the  expense  of  no  greater  quantity  of  steam 
and,  therefore,  of  heat.  The  saving  effected  by  the  expansive 
use  may  be  expressed  as  5,600  •*-  8,000  =  0.70  or  70  per  cent. 
Note,  however,  that  although  the  Fig.  10  arrangement  works 
the  more  economically  than  does  that  of  Fig.  9,  it  does  less 
total  work— 13,600  ft.  Ib.  as  against  16,000  ft.  Ib.  It  follows 
that  the  Fig.  10  cylinder,  to  do  the  same  amount  of  work  as 
in  Fig.  9,  would  have  to  be  increased  in  size  in  the  ratio  of 
16,000  to  13,600.  Or,  it  would  have  to  be  about  18  per  cent, 
larger.  The  conclusions  to  be  drawn  from  the  above  are: 

(1)  That  expansion  increases  the  ratio  of  work  done  to  heat  used. 

(2)  That  expansion  necessitates  a  larger  cylinder  for  a  given 
work  output.     Further  considerations  which  attend  expansive 
use  of  steam  are  given  in  Div.  10. 

NOTE. — THE  EXPANSIVE  USE  OF  STEAM  Is  NOT  DESIRABLE  IN 
ENGINES  OF  CERTAIN  CLASSES,  such  as  hoisting  engines,  steam  pumps, 
and  steam  hammers.  An  engine  which  uses  steam  expansively,  if 
stopped  in  a  position  where  the  admission  valve  is  closed,  cannot  be 
started  without  moving  the  engine  mechanism,  by  some  outside  means, 
until  the  valve  opens.  This,  of  course,  is  undesirable  in  engines  which 
must  be  frequently  stopped,  as  must  those  listed  above.  These  engines, 
therefore,  are  not  usually  so  made  as  to  use  steam  expansively. 

17.  To  Compute  The  Work  Done  Per  Double-Stroke 
By  Any  Steam  Engine,  use  the  following  formula,  which  is 
simply  the  mathematical  expression  of  the  rules  of  Sec.  14: 

(3)  W  =  AipLj8Pm  (ft.  Ib.  per  double  stroke) 

Wherein :  W  =  work  done  in  one  end  of  a  cylinder  per  double 
stroke  (Sec.  14),  in  foot  pounds.  Aip  =  area  of  piston,  exclu- 
sive of  any  rod,  see  note  below,  which  passes  through  the 
cylinder  end,  in  square  inches.  LJs  =  length  of  stroke,  in 
feet.  Pm  =  mean  effective  pressure  (Sec.  15),  in  pounds  per 
square  inch. 

NOTE. — THE  EFFECT  OF  ROD  AREA,  since  the  rod  area  subtracts  from 
the  total  area  upon  which  the  steam  can  act,  is  cared  for  by  subtracting 
the  area  of  the  rod  from  the  total  cross-sectional  area  of  the  cylinder 
whenever  a  rod  extends  through  the  cylinder  end  or  head.  Single-acting 
engines  (Sec.  14)  seldom  have  a  rod  extending  through  the  cylinder  head. 


14       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  1 

Double-acting  engines  may  have  a  rod  extending  through  one  cylinder 
head  or  they  may  have  rods  extending  through  both  heads.  Since  the 
area  of  the  piston  rod  seldom  exceeds  from  %  to  1%  per  cent,  of  the 
cylinder  area,  it  may  well  be  neglected  in  practical  problems  and  in  approx- 
imations. In  exact  determinations,  however,  it  must  be  considered. 

EXAMPLE.  —  A  single-acting  engine,  which  takes  steam  at  only  one  end 
and  has  no  rod  passing  through  the  head,  has  a  piston  10  in.  in  diameter 
and  a  stroke  of  30  in.  If  the  mean  effective  pressure  is  66  Ib.  per  sq.  in., 
what  work  is  done  per  double-stroke?  SOLUTION.  —  Substituting  in  For. 
(3):  W  =  AipLf8Pm  =  (10  X  10  X  0.785)  X  (30  +  12)  X  66  =  12,925.5 
ft.  Ib.  per  double-stroke. 

18.  To  Compute  The  Power  Developed  In  Any  Steam 
Engine,  the  elements  of  time  must  be  introduced  into  the 
work  equation  of  Sec.  17.  Since  power  is  the  rate  of  doing 
work  (see  the  author's  PRACTICAL  HEAT)  it  may  be  expressed 
in  foot  pounds  per  second  or  in  foot  pounds  per  minute  or  in 
B.  t.  u.  per  hour  and  so  on.  In  this  book,  power  will  usually 
be  measured  in  horse  power.  The  horse  power  is  equivalent  to 
550  ft.  Ib.  per  sec.  or  33,000  ft.  Ib.  per  min.  The  following 
formulas,  which  follow  from  the  preceding,  give  the  power 
which  is  developed  in  only  one  end  of  the  cylinder.  For  a 
double-acting  engine  compute  for  each  end  separately,  allow- 
ing for  the  piston-rod  area  if  necessary.  Then  add  the  two 
results. 
(4)  P  =  PmLjsAipN,  (ft.  Ib.  per  min.) 


Wherein:  P  =  power  developed  in  one  end  of  the  cylinder,  in 
foot  pounds  per  minute.  Pihp  =  power  developed  in  one  end 
of  the  cylinder  (indicated  power),  in  horse  power.  Pm  = 
mean  effective  pressure,  in  pounds  per  square  inch.  Lfs  = 
length  of  stroke,  in  feet.  Aip  =  area  of  piston,  exclusive 
of  the  area  of  any  rod  which  passes  through  the  cylinder  end, 
which  is  under  consideration,  in  square  inches.  Ns  =  number 
of  double  strokes  per  minute,  see  note  under  Sec.  14;  for  steam 
engines  with  rotative  crank  shafts:  N8  =  N  =  the  angular 
speed  of  the  crank  shaft,  in  revolutions  per  minute.  (Only 
engines  with  rotative  crank  shafts  will  be  considered  in  this 
book.) 


SEC.  19] 


PRINCIPLE  OF  THE  STEAM  ENGINE 


15 


EXAMPLE. — If  the  engine  of  the  example  of  Sec.  17  has  a  crank  shaft 
which  makes  100  r.p.m.,  what  is  its  indicated  power  in  foot  pounds  per 
minute  and  in  horse  power?  SOLUTION. — By  For.  (4) :  P  =  Pm 
LfSAipNs  =  WNS  =  12,925.5  X  100  =  1,292,550  ft.  Ib.  per  min.  By 
For.  (5):  Pap  =  P^L/aAip^/33,000  =  P/33,000  =  1,292,550  -^ 
33,000  =  39.2  h.p.  See  also  the  example  under  Table  20. 

19.  To  Compute  The  Approximate  Mean  Effective  Pres- 
sure of  a  simple  steam  engine  (Sec.  33)  when  an  indicator 
diagram  (Sec.  78)  cannot  be  obtained,  the  following  formula 
may    be    useful.     Since    engines    with    throttling    governors 
(Sec.  215)  do  not  take  steam  at  boiler  pressure  except  under 
very  heavy  load,  the  formula  can  only  be  used  for  such  engines 
when  it  is  known  that  the  governor  valve  is  wide  open. 

(6)  Pm  =  0.9[K(Pff  +  14.7)  -  Pa]  (pounds  per  square  inch 
Wherein:  Pm  =  the  approximate  mean  effective  pressure,  in 
pounds  per  square  inch.  K  =  a  constant,  as  found  from  Table 
20,  depending  on  the  apparent  cut-off.  Pg  =  the  pressure  of 
the  steam  in  the  engine's  supply  pipe,  or  the  boiler  pressure, 
in  pounds  per  square  inch  gage.  Pa  =  the  back  pressure  on 
the  engine,  in  pounds  per  square  inch  absolute;  for  non-con- 
densing engines  Pa  may  be  taken  at  17  Ib.  per  sq.  in.  abs.; 
for  condensing  engines,  Pa  is  found  from  the  condenser  vacuum 
gage  and  barometer  readings. 

20.  Table  Of  Constants  For  Use  In  Calculating  Approxi- 
mate Mean  Effective  Pressure. — The  values  of  K  tabulated 
below  are  those  to  be  used  in  For.  (6)  of  the  preceding  section. 


Cut-off 

K 

Cut-off 

K 

Cut-off 

K 

Frac- 
tion 

Per 
cent. 

Frac- 
tion 

Per 
cent. 

Frac- 
tion 

Per 

cent. 

H 

17 

0.545 

M 

37 

0.773 

H 

67 

0.943 

X 

20 

0.590 

% 

'40 

0.794 

Ko 

70 

0.954 

K 

25 

0.650 

H 

50 

0.864 

M 

75 

0.970 

Mo 

30 

0.705 

H 

60 

0.916 

H 

80 

0.981 

H 

33 

0.737 

K 

63 

0.927 

y8 

88 

0.993 

16       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  1 


NOTE. — In  this  table  the  fraction  or  percentage  cut-off  is  obtained  by 
dividing  the  distance  that  the  piston  has  travelled  from  the  beginning  of 
its  stroke  when  the  steam  is  cut-off,  by  the  whole  length  of  stroke;  that  is, 
it  is  the  apparent  cut-off,  Sec.  135. 

EXAMPLE. — Find  the  mean  effective  pressure  of  a  non-condensing 
engine,  which  cut-offs  at  one-half  stroke,  if  the  boiler  pressure  is  80  Ib. 
per  sq.  in.  gage.  If  the  engine  is  double-acting,  runs  at  320  r.p.m.,  has 
a  piston  7  in.  in  diameter,  and  has  a  10-in.  stroke,  what  is  its  horse  power? 
SOLUTION.— By  Table  20,  K  =  0.864  for  %  stroke.  Substituting  in 
For.  (6):  Pm  =  0.9  [K(Pa  +  14.7)  -  P.]  =  0.9  X  [0.864(80  +  14.7)  - 
17]  =  58.3  Ib.  per  sq.  in.  Then,  by  For.  (5) :  Pihp  =  PmLfSAipNs/33,QOO 
=  [58.3  X  (10  -^  12)  X  (7  X  7  X  0.785)  X  320]  -^  33,000  =  18.1  h.p., 
for  one  end.  Now,  since  the  engine  is  double-acting,  the  total  horse  power 
will  (disregarding  piston-rod  area)  be  twice  that  of  one  end  or:  total 
horse  power  -  2  X  18.1  =  36.2  h.  p. 

21.  The  Form  Of  The  Expansion  Line  For  Steam,  as  it 

expands  within  the  engine  cylinder,  is  different  for  different 


JT160 

|  .40 
£  120 
g  100 

%   80 

£ 
a   60 


!*> 

< 


lateral  Hyperbola 


'/abatic  Expansior 


Curve 


10    20    30    40    50    60    10    60    90    100   110    120   130  140 
Volume  Per  Pound   Of  Steam,    Gu.  Ft. 


Fia.  11. — Graphs  comparing  adiabatic  expansion  curve  and  equilateral  hyperbola  for 
Steam  expanding  from  165  Ib.  per  sq.  in.  abs.  to  2  Ib.  per  sq.  in.  abs. 

engines.  As  assumed  in  the  Rankine  cycle  (Sec.  8),  if  the 
cylinder  and  piston  were  of  non-heat-conducting  material 
the  expansion  would  be  adiabatic.  That  is,  the  steam  would 
suffer  no  gain  or  loss  of  heat  by  heat  transfer.  During  expan- 
sion the  heat  content  of  the  steam  would  decrease  at  the  same 
rate  as  that  at  which  the  steam  does  work  upon  the  piston. 
The  exact  form  of  the  expansion  curve  would  depend  some- 
what upon  the  initial  and  final  steam  pressures.  Since,  how- 
ever, no  cylinder  or  piston  is  non-heat-conducting,  the  form 
of  the  actual  expansion  line  will  differ  from  the  adiabatic 
curve.  Experiments  show  that  the  expansion  generally 


SEC.  21]          PRINCIPLE  OF  THE  STEAM  ENGINE  17 

follows  very  nearly  an  equilateral  hyperbola.     The  construc- 
tion of  the  equilateral  hyperbola  is  given  in  Sec.  108. 

EXAMPLE. — The  adiabatic  expansion  curve  for  steam  expanding  from 
165  Ib.  per  sq.  in.  to  2  Ib.  per  sq.  in.  is  plotted  in  Fig.  11.  An  equilateral 
hyperbola  is  also  plotted  alongside  it  (dashed). 

QUESTIONS  ON  DIVISION  1 

1.  What  is  the  primary  function  of  the  steam  engine? 

2.  How  is  heat  energy  derived? 

3.  How  is  mechanical  energy  transmitted?     How  heat  energy? 

4.  Draw  a  sketch  of  a  steam  engine  and  enumerate  the  principal  parts. 

5.  Explain    the    term    clearance.     Define   displacement   volume.     How   is    clearance 
usually  expressed?     What  is  piston  clearance?     How  is  it  measured? 

6.  Explain,   with  a  sketch,  the  operation  of  an  elementary  steam  engine  with  hand- 
operated    valves.     How    can    the    valves  be  made  to  operate  automatically?     Show 
with  a  sketch. 

7.  Show,  by  a  sketch,  the  form  of  a  single  valve  which  controls  the  steam  flow  to 
both  ends  of  a  cylinder. 

8.  In    what   forms  is  energy  available  for  man's  use?     In  what  forms  is  it  most  fre- 
quently employed?     How  is  energy  transformed  to  the  useful  forms? 

9.  State  the  mechanical  and  electrical-energy  equivalents  of  the  British  thermal  unit. 

10.  Why  cannot  an  engine  convert  into  work  all  of  the  heat  which  it  receives?     What 
becomes  of  that  which  is  not  abstracted? 

11.  Define    theoretical   efficiency.     Upon  what  does  the  theoretical  efficiency  of  an 
engine  depend?     Give  the  formula  for  theoretical  efficiency. 

12.  Explain  the  construction   and  operation  of  the  theoretically  most  perfect  steam 
engine.     Why  is  it  not  practical?     What  is  its  cycle  called? 

13.  Whence  does  a  steam  engine  derive  its' ability  to  do  work? 

14.  Into  what  two  classes  does  the  heat  which  an  engine  abstracts  from  the  steam 
first  divide?     Which  of  these  constitutes  a  direct  loss?     The  abstracted  heat  which  does 
not  constitute  a  direct  loss  is  how  used? 

15.  Draw  a  heat  balance  diagram  to  show  the  disposition  of  all  of  the  heat  which  an 
engine  receives. 

16.  Explain  what  distinguishes  an  efficient  steam  engine.     An  efficient  power  plant. 
Can  an  efficient  power  plant  be  made  up  of  inefficient  steam  engines?     Why? 

17.  Explain  how  steam  does  work  by  direct  pressure.     Define  net  pressure. 

18.  Explain  how  work  is  sometimes  required  to  drive  exhaust  steam  from  an  engine 
cylinder.     Define  effective  pressure.     Define  a  working  stroke. 

19.  Explain  how  steam  does  work  by  expansion.     Define  mean  effective  pressure. 
Explain,  with  a  diagram,  the  economy  of  using  steam  expansively.     What  classes  of 
engines  do  not  use  steam  expansively?     Why? 

20.  Give  the  formula  for  finding  the  net  work  done  per  double-stroke  by  the  steam 
upon  the  piston.     Explain  its  derivation. 

21.  Define  power.     What  are  its  units?     State  the  horse  power  formula  for  engines. 

22.  Give  the  formula  for  finding  the  approximate  mean  effective  pressure  of  a  steam 
engine.     To  what  classes  of  engines  may  it  be  applied?     Upon  what  three  variables 
does  the  mean  effective  pressure  depend? 

23.  What  form  does  the  expansion  line  take  for  steam  which  expands  in  an  actual 
engine  cylinder?     What  form  has  it  in  the  Rankine  cycle? 

PROBLEMS  ON  DIVISION  1 

1.  A  10-in.  by  12-in.  engine  has  a  clearance  volume  of  185  cu.  in.  at  the  head  end  and 
180  cu.  in.  at  the  crank  end.     If  the  piston  rod  is  1.5  in.  in  diameter,  what  are  the  clear- 
ances in  per  cent,  of  the  displacement  volumes? 
2 


18       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  1 

2.  A  steam  engine  is  supplied  with  dry  saturated  steam  at  a  pressure  of  160  Ib.  per 
sq.  in.    abs.     and  exhausts  steam   of  89  per  cent,  quality  at  17  Ib.  per  sq.  in.  abs. 
What  is  its  theoretical  efficiency? 

3.  A  double-acting  hoisting  engine  with  a  9-in.  -diameter  piston  and  12-in.  stroke  takes 
steam  (for  full  stroke.  Sec.  13)  at  125  Ib.  per  sq.  in.  gage  and  exhausts  at  4  Ib.  per  sq.  in. 
gage.     How  much  work  does  the  steam  do  per  working  stroke?     If  the  engine  is  running 
at  200  r.p.m.,  what  is  its  horsepower?     Neglect  piston-rod  area. 

4.  If  the  engine  of  Prob.  3  were  arranged  to  cut  off  at  H  stroke  what  would  be  its 
horse  power? 


DIVISION  2 


STEAM-ENGINE  MECHANISMS  AND  NOMENCLATURE 

22.  The  Classification  Of  Steam -Engine  Types  which  follows 
is  rearranged  from  an  outline  in  STEAM  POWER  by  Hirshfeld 
and  Ulbricht.     As  there  is  an  overlapping  of  the  various 
types,  it  would  be  impractical  to  discuss  engines  according  to 
this  table.     Hence  no  effort  will  be  made  to  do  so.     Defini- 
tions of  the  various  terms  employed  in  this  table  are  given 
in   following    sections.     These    are    then    followed    by    brief 
descriptions    of    some    other    frequently   used  steam-engine 
terms,  and  of  the  types  of  governors. 

23.  Table  of  Classifications  of  Steam-Engine  Types. 


Basis  of  classification 

Primary  subdivision 

Secondary  subdivision 

(1)  Cylinder  arrangement 

(A)  Single  cylinder 
(B)  Tandem 
(C)  Cross 
(Z>)  Duplex 
(E)  Opposed 
(F)  Angle 

(2)  Longitudinal  axis 

(A)  Vertical 
(B)  Inclined 
(C)  Horizontal 

(3)  Rotative  speed 

(A)  High  speed 
(B)   Medium  speed 
(C)  Low  speed 

(4)  Ratio  of  stroke  to  diame- 
ter 

(A)  Short  stroke 
(B)  Long  stroke 

(5)  Vai^e  gear 

(A)  Slide  valve 

(a)   D-slide  valve 
(6)  Balanced  valve 
(c)  Multiported  valve 
(d)  Gridiron  valve 
(e)  Piston  valve 

(B)  Corliss  valve 

(a)  Detaching 
(b)  Positively-operated 

(C)  Poppet  valve 

(a)  Detaching 
(b)  Positively-operated 

20      STEAM  ENGINE  PRINCIPLES  AND  PRACTICE      [Div.  2 


Basis  of  classification 

Primary  subdivision 

Secondary  subdivision 

(6)  Engine  mechanism 

(A)  Standard 
(B)  Back-acting 
(C)  Trunk-piston 
(D)  Oscillating-cylinder 

(7)  Steam  expansion 

(A)  Single  expansion 

(B)   Multi-expansion 

(a)  Compound 
(b)  Triple 
(c)  Quadruple 

(8)  Steam  flow 

(A)  Counter  flow 
(B)  Uniflow 

(9)  Steam  conditions 

(A)  Initial  pressure 

(a)   High  pressure 
(b)   Medium  pressure 
(c)  Low  pressure 

(B)  Initial  temperature 

(a)   High  superheat 
(b)  Low,  or  no  superheat 

(C)  Back  pressure 

(a)  Condensing 
(b)   Non-condensing 

Cylinder-- 
Piston  - 


-•Piston 
Valve 


24.  A  Vertical  Steam  Engine  (Fig.  12)  is  one  which  has  the 
center  line  of  its  cylinder,  M,  in  a  vertical  position. 

25.  A  Horizontal  Steam  Engine 
(Fig.    13)    is    one  which   has   the 
center  line,  CL,  of  its  cylinder  in 
a  horizontal  position. 

26.  An  Inclined  Steam  Engine 
(Fig.    14)    is   one   which   has    the 
center   lines,    CL,   of  its  cylinders 
inclined    from    the    horizontal    or 
vertical  position. 

27.  A  Side-Crank  Engine  (Figs. 
17  to  21)  is  one  which  has  its  crank 
attached  at  the  end  of  the  shaft 
overhanging  the  main  bearing.     In 
engines  of  this  type  the  crank,  C 
(Fig.    15),  is  generally  forged  as  a 
separate  part  and  fastened  securely 
to  the  shaft,  S. 

28.  A  Center-Crank  Engine  (Fig. 
12)  is  one  which  has  its  crank   located   between   the  crank- 


FIG.  12. — A  vertical  steam  engine. 


SEC.  29] 


STEAM  ENGINE  MECHANISMS 


21 


shaft   bearings.     In  this  type  of  engine,  the  crank,  C  (Fig. 
16),  is  generally  forged  as  part  of  the  shaft,  S. 


Flywheel  ~^ 
Connecting 


Crosshead'         'NN.  *•--_!  j_  .>**,;>" 
FIG.  13. — A  horizontal  steam  engine. 


Remote- 
Con  trolled 
Throttle 
Valve 


•Main 
Bearing 
Drum 
Shaft 

Cor/iss- 
Valve  Engine 


Steam  Supply' 

FIG.  14. — An  inclined  Corliss  engine  as  used 
for  large-capacity  mine  hoists. 


29.  A  Right -Hand  Engine  (Fig.  17)  is  a  side-crank  engine 
the  flywheel  of  which  is  mounted  on  the  right  side  of  the 


,--Crank  Pin 


FIG.  15. — Forged  crank  for  a  side- 
crank  engine. 


Counterweight  - 

FIG.  16. — Solid  forged  crank  and 
shaft  for  a  center-crank  engine. 


cylinder  axis,  CL,  as  viewed  from  the  head  end  of  the  cylinder, 
0. 


FIG.   17. — A  right-hand  engine. 


FIG.   18. — A  left-hand  engine. 


30.  A  Left-Hand  Engine  (Fig.  18)  is  a  side-crank  engine 
the  flywheel  of  which  is  mounted  on  the  left  side  of  the 
cylinder  axis,  CL,  as  viewed  from  the  head  end  of  the  cylinder, 
0. 


22       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  2 

31.  An  Engine  Is  Said  To  "Run  Over"  (Fig.  19)  when 
the  top  of  the  flywheel,  T,  is  turning  away  from  the  cylinder, 
C.  This  term  is  applied  only  .to  horizontal  and  inclined 
engines. 

NOTE. — THE  DIRECTION  OP  ROTATION  OF  A  VERTICAL  ENGINE  Is 
ORDINARILY  SPECIFIED  As  CLOCKWISE  OR  COUNTER-CLOCKWISE  as 
viewed  from  the  valve  side  of  the  engine.  Clockwise  (sometimes  called 
right-hand)  rotation  is  in  the  direction  of  motion  of  the  hands  of  a  clock. 
Counter-clockwise  (left-hand)  rotation  is  in  the  reverse  direction  of  clock- 
wise rotation.  Thus,  in  Fig.  19,  the  flywheel  is  turning  clockwise.  In 
Fig.  20,  the  flywheel  is  turning  counter-clockwise. 

NOTE. — STATIONARY  ENGINES  USUALLY  ARE  DESIGNED  To  "RUN 
OVER,"  so  the  pressure  between  the  crosshead  and  the  crosshead  guide, 


Direction  Of  Rotation 
Flywheel--^/, 
•Cylinder 




FIG.  19. — Engine  "running  over. 


Direction  Of  Rotcrtion- 

nywheeh 
•Cylinder 


FIG.  20. — Engine  "running  under. 


due  to  the  angularity  of  the  connecting-rod,  comes  on  the  lower  side  of 
the  crosshead  only,  and  also  so  the  belt,  which  usually  leads  away  from 
the  engine,  will  have  the  driving  pull  on  the  lower  side.  Hence  the 
direction  for  running  over  is  sometimes  referred  to  as  "  running  forward. 
Sometimes  the  term  "running  clockwise"  is  intended  to  mean  "running 
over, "  or  forward,  and  in  the  same  direction  as  the  hands  of  a  clock  to 
an  observer  viewing  an  engine  with  the  shaft  to  his  right  hand  and  the 
cylinder  to  his  left.  It  follows  that  the  terms  clockwise  and  counter- 
clockwise applied  to  an  engine  are  often  confusing,  as  the  direction  will 
appear  to  be  clockwise  to  a  person  standing  on  one  side  and  counter- 
clockwise to  one  standing  on  the  other  side.  Therefore  it  is  best  to 
confine  the  designations  of  directions  of  rotation  to  the  terms  "  running 
over"  and  "running  under.  " 

32.  An  Engine  Is  Said  To  "Run  Under"  (Fig.  20)  when  the 
top  of  the  flywheel,   T,  is  turning  toward  the  cylinder,  C. 
This    term    is    applied    only    to    horizontal    and    inclined 
engines. 

33.  A  Simple  Engine  (Figs.  12  and  21)  is  one  in  which  the 
conversion  of  the  heat  energy  of  the  steam  into  mechanical 


SEC.  34] 


STEAM  ENGINE  MECHANISMS 


23 


work  occurs  in  one  stage  or  step  only.  This  conversion  is 
brought  about  in  one  cylinder,  C  (Fig.  21),  only  and  by  using 
but  one  piston,  P. 


•Flywheel 


Cylinder^ 
Drain  Cock  -' 

Exhaust 
FIG.  21. — Simple  D-slide  valve  engine  with  fly-ball  governor. 

NOTE. — A  TWIN-CYLINDER  ENGINE,  SOMETIMES  CALLED  A  DOUBLE 
ENGINE,  (Fig.  22)  is  one  which  consists  of  two  simple-engine  cylinders 
which  are  placed  side  by  side  and  parallel,  and  whose  pistons  are  con- 
nected by  separate  connecting  rods  to  the  same  crank  shaft.  Twin 
cylinder  engines  are  widely  used  for  hoist- 
ing and  for  driving  heavy  machinery. 

34.  A  Compound   Engine   (Fig. 
23)  is  one  in  which  the  conversion 
of    the  heat  energy  of  the  steam 
into  work  takes  place  in  two  stages 

or  steps.  Steam  enters  the  high-  FIG.  22.— Plan  view  of  a  twin-cyi- 
pressure  cylinder,  H,  where  it  inder  engine- 

undergoes  the  first  stage  of  its  expansion.  The  steam  is  then 
exhausted  into  the  receiver.  From  the  receiver  it  passes  into 
the  low-pressure  cylinder,  L,  where  the  second-stage  expansion 
occurs. 

35.  A  Tandem-Compound  Engine  (Fig.  23)  is  a  compound 
engine  with  its  two  cylinders,  H  and  L,  along  a  common  axis, 


Flywheel-' 


24       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  2 

or  "in  line."  A  tandem-compound  engine  has  only  one 
crosshead  and  one  connecting  rod  and  has  both  of  its  pistons 
on  a  common  piston  rod,  R. 

36.  A  Cross-Compound  Engine   (Fig.  24)  is  a  compound 
engine  which  has  two  parallel  cylinders,  H  and  L,  on  the 


Steam 


High- Pressure  Piston 
FIG.  23. — A  tandem-compound  engine  (Ball  Engine  Company). 

same  side  of  the  crank  shaft,  each  piston  being  connected  by 
a  separate  connecting  rod  to  the  one  crank  shaft. 

37.  A  Duplex-Compound  Engine  (Fig.  25)  is  a  compound 
engine,  the  cylinders  of  which  are  parallel  and  adjacent  to 
each  other  as  shown.  H  is  the  high-pressure  cylinder  con- 


,'High  -Pressure  Cylinder 
•-Path  of  Steam 


Exhaust      /Low-Pressure  Cylinder 
Pipe^        /   Low-Pressure      Crank  Disk, 


Flywheel' 
V     'r-- Low -Pressure  Cylinder 

Fia.  24. — Diagrammatic  plan  view 
of  a  cross-compound  engine. 


'H/'ffh-Pressure\  ^-High-Pressure  Piston  Rod 
Cylinder  ^^eam  supp/u  Pipe 

FIG.  25. — A  duplex-compound  engine. 


nected  to,  L,  the  low-pressure  cylinder.  The  piston  rods, 
RI  and  R2,  are  connected  to  the  same  crosshead,  C.  This 
type  of  engine  occupies  the  same  floor  space  as  does  a  simple 
engine,  but  has  the  advantages  of  a  compound  engine  with 
respect  to  economy  of  steam  consumption  (Div.  8). 


SEC.  38] 


STEAM  ENGINE  MECHANISMS 


25 


38.  An  Angle -Compound  Engine  (Fig.  26)  is  a  compound 
engine  which  has  its  two  cylinders,  A  and  B,  placed  at  right 
angles  to  each  other.  The  connecting  rods  are  connected 
to  the  same  crank  shaft  and  usually  to  the  same  crank  pin. 


,  Low-Pressure 
i.      Cy/ina'er 


f  -Flywheel 


High-Pressure    ^Intermediate  Cylinder 
Cylinder*  ;     -^Low- Pressure  Cylinder 

|^>|H|>:;:.->llKllllx-^ 

Flywheel. 


•''  High- Pressure        \ 
Cylinder-1' 

FIG.  26. — Elevation    of    an    angle- 
compound  engine. 


'/////  7///// 

Bearing—-    *"  ; 


FIG.  27. — Elevation  of  a  triple-expansion 
engine. 


39.  A  Triple -Expansion  Engine,  Sometimes  Called  A 
Triple -Compound  Engine  (Figs.  27  and  28)  is  one  in  which 
the  heat  energy  of  the  steam  is  converted  into  work  in  three 
successive  stages  and  in  at  least  three  separate  cylinders,  as 


High -Pressure      ,  Direct  ion  of 
Cylinder^         /  Steam  Flow 

'•     •*         .Frame         Bearing^ 


Cylinders 

High  .First  Intermediate 

Pressure,         j    .Second 


\  Intermediate   •'  Pressure 


FIG.  28. — A  plan  view  of  a  triple- 
expansion  engine  with  two  low-pressure 
cylinders. 


Outboard    ,-  ( 
Bear -ing •-'';    • 


FIG.     29. — Elevation    of     a    quadruple- 
expansion  vertical  engine. 


A,  B,  and  C,  Fig.  27.  A  triple-expansion  engine  with  four 
cylinders  is  shown  in  Fig.  28  in  which  A  is  the  high-pres- 
sure, B  is  the  intermediate,  and  C  and  D  are  the  low-pressure 
cylinders. 


26       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  2 


40.  A  Quadruple  -Expansion  Engine,  Sometimes  Called  A 
Quadruple  -Compound  Engine  (Fig.  29)  is  one  in  which  the 
heat  energy  of  the  steam  is  converted  into  work  in  four  succes- 
sive stages,  and  usually  in  four  separate  cylinders,  A,  B, 
C,  and  D.  A  is  the  high-pressure  cylinder,  B  the  first  inter- 
mediate cylinder,  C  is  the  second  intermediate  cylinder,  and 
D  the  low-pressure  cylinder. 

41.  A  Slide  Valve  (7,  Fig.  30) 
is  a  positively  operated  valve 
which  has  a  reciprocating  motion 
and  which  slides  upon  a  face,  S, 
called  its  seat.  As  the  valve 
slides  back  and  forth  on  its  seat, 

j£     UnCOVCrS    ports    (holes    in    the 


'-Cylinder  Port 


Cylinder  Port     ' 


FIG.    30. — Cross-section    of   a 
valve  and  its  seat. 


D-siide  sea£  leading  to  either  end  of  the 
cylinder)  placing  these  ports  into 
communication  with  either  the  supply  or  exhaust  pipe.  There 
are  two  principal  types  of  slide  valves:  —  (1)  Flat  type,  Figs.  21 
and  30.  (2)  Piston  type,  Figs.  12  and  33. 

NOTE.  —  STEAM-ENGINE  VALVES  ARE  DISCUSSED  IN  DETAIL  IN 
DIVISIONS  4  and  5.  The  illustrations  and  definitions  following  are 
merely  to  acquaint  the  reader  with  the  several  valve-types  in  their  more 
simple  forms. 

42.  A  D  -Slide  Valve  (Figs.  21  and  30)  is  a  flat  valve,  V 
Fig.  30,  having  a  cross-sectional 
form  similar  to  the  letter  "D." 
The  pressure  of  the  steam  in  the 
steam  chest  forces  the  valve 
against  its  seat,  S,  preventing 
leakage  of  the  steam  between  V 
and  S.  In  cases  where  the  D- 
valve  is  very  large,  the  force 
due  to  the  steam  pressure  on  the 


Balancing 
H°le         Steam 
Space 


Wand  v 


Valve ; 


Space       I      Seat 
'Cylinder  Ports' 

FIG.  31. — Balanced,  flat,  D-slide  valve. 

valve  is  apt  to  be  very  great  and 

cause  excessive  friction  at  the  rubbing  surfaces.     To  prevent 

excessive  resistance  due  to  this  friction,  balanced  valves  are 

used. 

43.  A  Balanced  Slide  Valve  (Fig.  31)  is  one  in  which  the 
bearing  pressure  of  the  valve,  V,  upon  its  seat  due  to  the 


SEC.  44] 


STEAM  ENGINE  MECHANISMS 


27 


pressure  of  the  steam  is  minimized  by  some  special  design, 
which  usually  permits  the  same  steam  pressure  to  act  on  both 
sides  of  the  valve;  for  explanation  see  Sec.  139.  The  piston 
valve,  Fig.  12,  is  also  a  balanced  slide  valve.  •; 

44.  A  Multiported  Valve  (Fig.  32)  is  one  in  which  there 
are  two  or  more  passages  through  which  steam  can  flow  into 
or  out  of  the  cylinder  ports.  Multiported  valves  permit 
shorter  valve  travel  and  quicker  opening  and  closing  of  the 
ports  than  is  possible  with  common  (single-ported)  slide  valves. 
In  Fig.  32,  the  ports,  H,  are  the  cylinder  ports;  and  the  port, 
L,  is  the  exhaust-steam  port.  Multiported  slide  valves  are  also 
frequently  made  in  the  " balanced"  form  (see  Div.  4). 


Tai-f        (Exhaust 

Bearing*  ' 


'From       _ . 
Boiler,'?'5?™ 
,'    Valve 


Valve 
Sfem 


*  Cylinder  Ports'' 
FIG.  32. — Multiported  slide  valve. 


^Cylinder 

FIG.  33. — Section  of  cylinder  with  a  piston 
valve.  (Chandler  and  Taylor  Company.) 


45.  A  Piston  Slide  Valve  (Fig.  33)  is  a  cylindrical-shaped 
valve,  V,  which  is  given  reciprocating  motion  in  a  cylindrical 
seat,  S.     Its  action  is  very  similar  to  that  of  the  simple  D- 
valve.     There  are  these  differences,  however:  (1)  The  piston 
valve  is  "balanced."     (2)  The  piston  valve  usually  is  of  the 
"center  admission"  construction,  whereas  D-valves  usually  are 
of  the  "center  exhaust"  construction.;  see  Sec.  136. 

NOTT. — PISTON  SLIDE  VALVES  ABE  PARTICULARLY  DESIRABLE  IN 
VERTICAL  ENGINES,  since,  by  making  the  upper  portion  of  the  valve  of 
greater  diameter  than  the  lower  portion,  it  is  thereby  possible  to  balance 
the  weight  of  the  valve  and  its  valve  rod  and  thus  minimize  the  wear 
on  the  eccentric. 

46.  A  Riding-Cut-off  Valve  (Fig.  34)  is  one  having  at  least 
two  moving  parts,  each  controlled  by  a  separate  eccentric 


28       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  2 


Steam 
Chest 

,  Hand  wheel For        '.     Riding- 
^  Adjusting  Cut-Off  '    Cut-Off  \blve 


"Cul/nder 


Lynn 
Port 


^Main    ^-Exhaust 
Valve       Port 


(see  Div.  4).  In  Fig.  34,  M  is  the  main  valve  controlling  the 
points  of  admission,  compression,  and  release;  and  R  is  the 
cut-off  valve  riding  upon  the  main  valve,  and  controlling  only 
the  point  of  cut-off  (Sec.  135). 

NOTE. — THE  POINT  IN  THE  STROKE 
AT  WHICH  THE  CUT-OFF  VALVE  CUTS 
OFF  may  be:  (1)  Fixed,  in  which  case 
the  cut-off  valve  is  neither  hand  ad- 
justable nor  governor-operated.  (2) 
Variable,  in  which  case  the  cut-off 
valve  may  be  either  hand-adjustable 
or  governor-operated.  With  a  hand- 
adjustable  cut-off  valve,  the  point  of 
cut-off  may  be  adjusted  to  any  required 
point,  while  the  engine  is  running; 
thereby  the  speed  of  the  engine  can 

be  changed  for  a  given  load  or  for  a  changed  load  the  point  of  cut-off 
may  be  altered  to  that  which  is  most  economical  or  which  will  give  the 
desired  speed.  With  a  governor-operated  cut-off,  the  advance-angle  of 
an  eccentric  associated  with  the  flywheel  governor  changes  automatically 
the  cut-off  to  maintain  the  engine  speed  constant  with  varying  load. 

47.  A  Gridiron  Valve  (Fig.  35)  is  a  reciprocating  valve  which 
has  the  form  of  a  gridiron  or  grating.  In  Fig.  35,  the  riding- 
cut-off  valve  and  the  main  valve,  M ,  are  both  of  the  gridiron 
type.  The  valve  seat,  S,  has  long  rectangular  openings 
between  the  little  bars  just  as  have  the  valves  themselves. 

Main      Steam  ,'Riding- 

Va/ve,     Space*  [Cut-Off  Valve    ,'VWVW 

: — Stem 


FIG.  34. — Section   of   a   Meyer  riding- 
cut-off   valve. 


FIG.  35. — Section  of  a  cylinder  with  a  grid- 
iron valve  (Mclntosh  and  Seymour  valve). 


FIG.  36. — Single-ported  Corliss  valves. 


Evidently,  then,  gridiron  valves  are  multiported  valves  with 
a  large  number  of  ports. 

48.  A  Corliss  Valve  (Figs.  36  and  37)  is  a  valve  the  ends 
of  which  are  cylindrical  and  which  oscillates  about  its  axis 
in  a  cylindrical  cavity  or  seat  at  right  angles  to  the  engine 


SEC.  48] 


STEAM  ENGINE  MECHANISMS 


29 


Admission 
Valve-. 


'Steam  Supply  ^Ac/mission 

Valve 


Exhaust  Valve  ^ 

''Steam  Exhaust 

FIG.  37. — Section  of  cylinder  with  double-ported  Corliss  valves. 

-  'Steam-Supply  Pipe 


-Throttle  Valve 


"'Exhaust  Pipe 
FIG.  38. — Chuse  positively-operated  Corliss-valve  mechanism 


30       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  2 

cylinder  axis.  The  cylinder  ports  are  opened  or  closed  by 
this  oscillatory  motion.  Corliss  valves  are  employed  two  to  a 
cylinder  end — one  for  admitting  steam  to  the  cylinder,  the 
other  for  exhausting  the  spent  steam  from  the  cylinder.  An 
engine  with  Corliss  valves  is  therefore  a  four-valve  engine. 
Corliss  valves  may  be  either  single-ported  (Fig.  36)  or,  as 
more  commonly  constructed,  multiported  (Fig.  37). 

49.  A    Positively-Operated,    Or    Non-Releasing,    Corliss- 
Valve  Mechanism  (Fig.  38)  is  one  in  which  the  admission 


FIG.  39. — Detaching  Corliss-valve  mechanism. 

valves,  A,  and  the  exhaust  valves,  E,  are  at  all  times  positively 
connected  to,  and  under  the  influence  of,  the  valve-operating 
(eccentric)  mechanism  to  which  they  are  linked  by  the  reach 
rods  B  and  C. 

50.  A  Detaching,  Or  Releasing,  Corliss -Valve  Mechanism 
(Fig.  39)  is  one  in  which  the  admission  valves,  A,  are  not 
positively  connected  to,  nor  under  the  influence  of,  the  eccen- 
tric mechanism  except  when  these  valves  are  open.  A  dash- 


SEC.  51] 


STEAM  ENGINE  MECHANISMS 


31 


pot  mechanism,  D,  provides  a  suction  for  quickly  closing 
the  steam  valves  as  soon  as  they  are  detached  from  the  eccen- 
tric mechanism.  Detachment  is  effected  by  releasing  a  snap- 
catch,  C,  which  is  controlled  by  the  governor.  The  exhaust 
valves,  E,  are  positively  connected  to  the  eccentric  mechanism 
at  all  times. 

51.  A  Poppet  Valve  (Figs.  40,  41,  and  42)  is  a  circular  valve, 
V,  Fig.  40,  having  an  opening  and  closing  movement  perpen- 
dicular to  its  seat,  S,  and  which  allows  steam  to  flow  under  or 
through  it.  This  type  of  valve  effects  a  large  port-opening 

with  a  small  valve-lift  and  is  free  of 
the  friction  occurring  with  valves 
which  slide  upon  their  seats.  Pop- 
pet valves,  on  account  of  their  sym- 
metrical construction  and  small  size, 
are  well  adapted  for  use  with  high- 
temperature  superheated  steam. 


..-Valve 
Bonnet 


^Piston 


FIG.  40. — Section  of  cylinder  with 
single-seated  poppet  admission 
valve. 


//C  y  I  i  n  d  e  r 

*5f  earn  Space  to  Cylinder 

FIG.  41. — Half-section  of  end  of  Nordberg- 
engine  cylinder  showing  positively-operated 
poppet  admission  valve. 


52.  A  Positively-Operated  Poppet  Valve  (Fig.  41)  is  one 
that  is  positively  opened  and  closed  by,  and  at  all  times 
under  the  influence  of,  the  valve-operating  (eccentric)  mechan- 
ism.    In  Fig.  41,  V  is  the  poppet  valve  and  M  the  eccentric 
rod  from  an  eccentric  on  a  lay-shaft  which  is  located  on  the 
side  of  the  engine  and  parallel  to  the  cylinder  axis. 

53.  A  Detaching,  Or  Releasing,  Poppet  Valve  (Fig.  42)  is 
one  that  is  opened  by  the  eccentric  mechanism,  but  is  closed 
by  a  spring,  dash-pot,  or  other  mechanism;  the  valve  is,  there- 


32       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  2 

fore,  under  the  direct  influence  of  the  eccentric  mechanism 
only  during  the  opening  period.  In  Fig.  42,  V  is  the  poppet 
valve,  S  the  valve-closing  spring,  and  M  the  eccentric  rod 
from  a  lay-shaft  eccentric. 

54.  A  Single-Valve  Engine  (Figs.  12  and  21)  is  one  in 
which  one  valve  controls  both  steam  admission  and  exhaust 
for  both  ends  of  the  cylinder.  Thus,  engines  with  D-slide 
valves,  whether  single  or  multiported,  balanced  or  unbalanced, 
and  engines  with  simple  piston  valves  are  all  single-valve 
engines. 

Valve-Opening 

Roller 


FIG.  42. — Half-section  of  a  Hamilton-engine  cylinder  with  detaching-poppet  admission 

valve. 


55.  A  Multi-Valve  Engine  (Fig.  37)  is  one  in  which  more 
than  one  valve  is  employed  for  admitting  and  exhausting 
steam  at  the  two  ends  of  the  cylinder.     Thus,  all  Corliss, 
poppet,  and  gridiron-valve  engines  are  of  this  type. 

56.  A  Short-Stroke  Engine  is  one  the  stroke  of  which  is 
less  than  the  diameter  of  its  cylinder.     For  example,  an  engine 
which  has  a  cylinder  12  in.  in  diameter  and  a  10-in.  stroke  is  a 
short-stroke  engine. 

57.  A  Long-Stroke  Engine  is  one  the  stroke  of  which  is 
greater  than  the  diameter  of  its  cylinder.     Thus  an  engine 
which  has  a  cylinder  7  in.  in  diameter  and  a  10-in.  stroke  is  a 
long-stroke  engine. 

58.  A   Counterflow,   Or   Double-Flow,   Engine    (Figs.   43 
and  44)  is  one  in  which  the  direction  of  steam  flow  in  its 
cylinder  on  the  exhaust  stroke  is  opposite  to  the  direction 
of  steam  flow  during  the  admission  stroke.     Thus  in  Fig.  43, 
steam  is  shown  entering  the  cylinder  and  flowing  toward  the 


SEC.  59] 


STEAM  ENGINE  MECHANISMS 


33 


right.     In  Fig.  44,  the  steam  is  being  exhausted  and,  as  is  seen, 
must  flow  in  the  opposite  direction  or  toward  the  left. 


Exhaust 


Cylinder 
Port 


--Steam-Supply 
Pipe 

; Steam  Chest 
,D-Va/ve 

,Valve 


-Steam  -Supply 
Pipe 

Steam  Chest 
D- Valve 


-Valve 
Stem 


^Piston       

Direction  of  Admission-Steam  Flow 

FIG.  43.  —  Showing  direction  of 
steam  flow  into  an  engine  cylinder 
employing  the  counterflow  principle. 


'Direction  of  Exhaust-Steam  flow 


FIG.  44. — Showing  direction  of  steam 
flow  during  exhaust  from  a  cylinder 
employing  the  counterflow  principle. 


NOTE. — CERTAIN  ENGINES  WITH  SEPARATE  ADMISSION  AND  EXHAUST 
VALVES  ARE  ALSO  COUNTERFLOW  ENGINES,  if  the  exhaust  valves  take 
the  steam  out  of  the  cylinder  at  its  end.  Thus,  the  Corliss  engine  (Fig. 
37)  is  a  counterflow  engine. 


Cylinder 
Jacket ^ 

Direction  of  \ 

,' Admission-Steam  Flow     '„ 


FIG.  45. — Showing  direction  of  steam  flow  into  a  uniflow-engine  cylinder. 

59.  A  Uniflow  Engine  (Figs.  45  and  46)  is  one  in  which  the 
steam  flows  in  only  one  general  direction  in  the  cylinder. 


34       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  2 


The  direction  of  steam  flow  during  the  exhaust  period  is  the 
same  as  during  the  admission  period.     Fig.  45  shows  steam 


...-Valve 
'      Bonnet 


Cylinder 

Valve  Jacket 

Direction  of  Exhausf- 
: Steam  Flow 


"Steam  Supply 


'Steam  Exhaust 


Crank 
Shaft, 


Steam 


Air  Discharge 


FIG.  46. — Showing  direction  of  steam  flow  during  exhaust  from  a  uniflow-engine 

cylinder. 

being  admitted  into  a  uniflow  engine  cylinder  and  flowing 
toward  the  right.  Fig.  46  shows  the  same  steam  being  ex- 
hausted from  the  cylinder  and  also  flowing  toward  the  right. 

60.  A  Standard  Crank-Mechanism  (Fig.  21)  is  one  consist- 
ing of  a  cylinder,  C,  a  piston,  P,  a  piston  rod,  R,  a  crosshead, 

a  connecting  rod,  L,  a  crank,  B, 
and  a  crank  shaft,  M — and  in 
which  the  crosshead  is  located 
between  the  cylinder  and  the 
crank  and  crank  shaft. 

61.  A     Back-Acting     Crank- 
"•connecting  Rod  Mechanism  (Fig.  47)  consists  of 

**"**  the  same  principal  parts  as  the 

FIG.    47. — A    double-connecting-rod, 

back-acting  crank-mechanism  as  applied  standard  crank-mechanism;  in 
to  air  compressors.  the  back-acting  crank-mechan- 

ism,  however,  both  the  crank  shaft,  S,  and  the  cylinder,  C, 
are  always  on  the  same  side  of  the  crosshead,  H.  This 


SEC.  62] 


STEAM  ENGINE  MECHANISMS 


35 


Wrist 
Pin  — 

Flywheel, 


mechanism,  will  usually  necessitate  either  two  piston  rods  or 
two  connecting  rods,  or  a  combination  of  two  piston  rods  and 
two  connecting  rods. 

62.  A  Trunk -Piston  Mechanism 
(Fig.  48)  is  one  employing  an  un- 
usually long,  or  trunk  piston,  P, 
in  which  one  end  of  the  connect- 
ing rod  is  pivoted  on  a  pin,  thus 
rendering  unnecessary  the   cross- 
head    used    in    other    types    of 
steam-engine     mechanisms.     En- 
gines   with    trunk     pistons     are 
single-acting.     That  is,  the  steam 
for  them  is  admitted  to,  and  does 
work    on,    only   one   side   of  the 
piston.     Internal    combustion  FIG. 
(automobile,     etc.)     engines    are 
usually  of  the  trunk-piston  type. 

63.  An  Oscillating-Cylinder  Engine   (Fig.  49)  is  one,  the 
mechanism  of  which  consists  of  a  cylinder,   C,   pivoted  in 


.-Flywheel 


48. — Trunk-piston  mechanism 
of  the  Model  Acme  engine.  (Auto 
matic  Furnace  Co.,  Dayton,  O.) 


,Z?  -Slide  Valve 


r  Pi  voted 
,''  Cylinder 


~~  Bearing 
FIG.  49. — An  old  engine  of  the  oscillating-cylinder  type.' 

bearings,  B\  a  piston  and  piston  rod,  R]  a  crank,  L;  and  a  crank 
shaft,   S.     In  this  type  of  engine,   the   oscillating  cylinder 


36       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  2 


takes  the  place  of  the  connecting  rod  and  crosshead  employed 
in  the  standard  crank-mechanism. 

64.  A  Condensing  Engine  is  one  which  normally  operates 
on  an  absolute  back  (exhaust)   pressure  which  is  less  than 
that  of  the  atmosphere.     The  back  pressure  is  reduced  by 
condensing  the  exhaust  steam  by  the  use  of  some  condensing 
device  (Div.  9). 

65.  A  Non-Condensing  Engine  is  one  which  operates  on  a 
back  (exhaust)  pressure  equal  to,  or  greater  than,  atmospheric 
pressure. 

66.  A  High-Speed  Engine  is  one  which  operates  at  a  speed 
of  about  200  r.p.m.  or  more. 

67.  A  Medium-Speed  Engine   is   one   which   operates  at 
some  speed  between  about  110  and  200  r.p.m. 


Note:  Exhaust  Valves  are  on 
Opposite  Side  of  Cylinder  and 
Not  Shown 

Steam 
f  Valve 


Governor^ 


^^^^^ 


Shaft  Extending  to  Other  Side  of 
Engine,  Operates  Exhaust  Valves 


FIG.  50. — An    engine    equipped    with    a  variable-cut-off  valve-mechanism. 

Allen  engine.) 


(Porter- 


68.  A  Low-Speed  (Or  Slow-Speed)  Engine  is  one  which 
operates  at  a  speed  of  100  r.p.m.  or  less. 

69.  A  High-Pressure  Engine  is  one  which  takes  steam  at 
its  throttle  at  a  pressure  greater  than  225  Ib.  per  sq.  in.  gage. 

70.  A  Medium-Pressure  Engine  is  one  which  takes  steam 
at  its  throttle  at  some  pressure  between  80  Ib.  and  225  Ib. 
per  sq.  in  gage. 

71.  A  Low-Pressure  Engine  is  one  which  takes  steam  at 
the  throttle  at  a  pressure  less  than  80  Ib.  per  sq.  in.  gage. 

72.  A  Fixed-Cut-Off  Engine  (Fig.  21)  is  one  in  which  the 
point  of  cut-off  remains  constant  throughout  all  ranges  of 
load  and  speed.     The  eccentric,  E,  is  fixed  to  the  shaft,  M. 
Therefore,   the   eccentric   rod,   F,  valve  stem,  S,  and  valve 


SEC.  73] 


STEAM  ENGINE  MECHANISMS 


37 


always  have  the  same  motion  relative  to  the  engine  cylinder 
and  valve  seat.  That  is — their  relative  motion  is  independent 
of  the  engine  load  or  speed. 

73.  A  Variable-Cut-Off  Engine  (Fig.  50)  is  one  in  which 
the  point  of  cut-off  varies  with  each  change  of  load  or  speed. 
In  Fig.  50,  as  the  engine  speed  increases,  the  governor  rod, 
R,  lowers  the  link  block,  B,  thus  diminishing  the  travel  of 
the  steam  rod,  S,  and  the  steam  valves,  Vi  and  F2.     By  means 
of  this  mechanism  the  point  of  cut-off  varies  with  different 
speeds  and  hence  with  different  loads;  see  following  sections 
on  governors. 

74.  A   Steam -Engine   Governor    (Figs.    51    and   52)    is   a 
device  which  changes  the  steam  input  to  an  engine  to  meet 


Flywheel 


FIG.  51. — Typical  shaft  governor. 

the  varying  demands  of  different  engine  loads,  and  at  the  same 
time  maintains  the  engine  speed  as  nearly  constant  as 
possible.  (See  Divisions  6  and  7.)  Steam-engine  governors 
are  of  two  general  types — (1)  Shaft  type,  Fig.  51.  (2)  Fly-ball 
type,  Fig.  52. 

75.  A  Shaft  Governor  (Fig.  51;  see  also  Div.  7)  is  one 
which  rotates  with  the  flywheel  in  a  plane  perpendicular  to 
the  crank-shaft  axis.  In  this  type  of  mechanism,  weights, 
W  and  Wi,  are  rotated  with  the  flywheel,  F.  Rotation  of  these 
weights  introduces  centrifugal  or  inertia  forces  which 
act  against  the  pull  of  springs,  S,  attached  to  F.  The  position 
of  the  weights  depends  upon  these  forces  which  are  proportional 
to  the  engine  speed.  The  position  on  the  shaft  of  the  eccentric, 
E,  is  varied  by  the  movement  of  the  weights  which  fly  outward 


38       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  2 


as  the  flywheel  speed  increases.  Since  the  relative  position 
of  the  eccentric  on  the  shaft  controls  the  valve  action,  a 
governor  of  this  type  will  perform  the  necessary  functions 
as  given  in  the  preceding  section.  See  Div.  7  for  further 
discussion  of  shaft  governors. 

76.  A  Fly-Ball  Governor  (Figs.  50  and  52;  see  also  Div.  6) 
is  one  in  which  two  or  more  " fly-balls"  rotate,  usually  in  a 
horizontal  plane.  Rotation  introduces  centrifugal  forces 
which  hold  the  balls  away  from  the  axis  of  rotation.  Suitable 

mechanism  affords  a  relation  be- 
tween the  position  of  the  balls 
and  the  amount  of  steam  fed 
to  the  engine.  In  Fig.  52,  the 
position  of  the  fly-balls,  G  and 
Gij  fixes  the  amount  of  opening 
of  the  throttle  valve,  V,  thus 
regulating  the  steam  supply  to 
the  engine.  Since  the  governor 
pulley,  P,  is  belted  to  the 
engine  shaft  (see  Fig.  21),  the 
fly-ball  positions  depend  upon 
the  engine  speed.  As  the  load 
increases,  the  engine  speed 
begins  to  decrease.  The  gov- 
ernor opens  the  throttle  valve 
and  thereby  again  increases  the 
engine  speed.  Likewise  when  the 
FIG.  52.— Section  of  a  typical  fly-bail  load  decreases,  the  engine  speed 

increases  and  the  goveror  closes 

the  throttle  valve  thereby  maintaining  the  speed  practically 
constant. 

QUESTIONS  ON  DIVISION  2 

1.  How  are  engines  classified  as  to: 

(a)  Cylinder  arrangement? 

(b)  Longitudinal  axis? 

(c)  Rotative  speed? 

(d)  Ratio  of  stroke  to  diameter? 

(e)  Valve  gear? 

(/)  Engine  mechanism? 
(g)  Steam  expansion? 
(h)  Steam  flow? 
(i)  Steam  conditions? 


SEC.  76]  STEAM  ENGINE  MECHANISMS  39 

2.  What  is  a  vertical  engine?     A  horizontal  engine?     An  inclined  engine? 

3.  Explain  the  chief  difference  between  a  side-crank  and  a  center-crank  engine. 

4.  What  is  a  right-hand  engine?     A  left-hand  engine? 

5.  When  is  an  engine  said  to  run  "over"?     To  run  "under"? 

6.  Explain  fully  the  meaning  of  the  following  terms: 

(a)  A  simple  engine. 

(6)  A  compound  engine. 

(c)  A  tandem-compound  engine. 

(d)  A  cross-compound  engine. 

(e)  A  duplex-compound  engine. 
(/)  An  angle-compound  engine. 
(g)  A  triple-expansion  engine. 

(h)  A  quadruple-expansion  engine. 

7.  What  is  a  slide  valve? 

8.  What  is  a  D-slide  valve? 

9.  Describe  and  give  the  features  of  a  balanced  slide  valve. 

10.  What  is  a  multiported  valve? 

11.  Describe  the  piston  slide  valve. 

12.  Describe  the  riding-cut-off  valve. 

13.  What  is  a  gridiron  valve?  * 

14.  Describe  fully  the  features  of  the  Corliss  valve. 

15.  What  is  the   chief  difference  between  a  positively-operated  and  a   detaching 
Corliss- valve  mechanism? 

16.  Describe  the  principle  of  operation  of  a  poppet  valve. 

17.  Explain  the  difference  between  a  positively-operated  and  a  detaching  poppet 
valve. 

18.  What  is  a  single-valve  engine? 

19.  What  is  a  multi- valve  engine? 

20.  When  is  an  engine  said  to  have  a  "short  stroke"?     A  "long  stroke"? 

21.  What  is  the  difference  in  principle  between  a  counterflow  engine  and  a  uniflow 


engine 


22.  Describe  the  following  engine  mechanisms: 
(a)  Standard  crank-mechanism. 

(6)  Back-acting  crank-mechanism. 

(c)  Trunk-piston  mechanism. 

(d)  Oscillating-cylinder  mechanism. 

23.  What  is  a  condensing  engine? 

24.  What  is  a  non-condensing  engine? 

25.  Give  the  speed  ranges  for:   (a)  A  high-speed  engine,      (b)  A  medium-speed  engine, 
(c)  A  low-speed  engine. 

26.  Give  the  steam-pressure  ranges  for:  (a)  A  high-pressure  engine.     (6)  A  medium- 
pressure  engine,     (c)  A  low-pressure  engine. 

27.  What  is  a  fixed-cut-off  engine? 

28.  What  is  a  variable-cut-off  engine? 

29.  Explain  the  purposes  of  a  steam-engine  governor. 

30.  What  is  a  shaft  governor? 

31.  Describe  the  fly-ball  governor 


DIVISION  3 

STEAM-ENGINE  INDICATORS  AND  INDICATOR 
PRACTICE 

77.  The  Steam-Engine  Indicator  (Fig.  53)  is  simply  an  in- 
strument which  records  graphically  on  an  "indicator  diagram" 
(D,  Fig.  54)  the  variations  of  pressure  within  an  engine 
cylinder,  as  the  engine  piston  occupies  different  positions 


Cap- 


Handle-^ 


FIG.  53. — External  view  of  a  Thompson  indicator  without  reducing  motion.     (American 
Steam  Gage  and  Valve  Co.) 

throughout  its  stroke.  It  might  well  be  called  a  recording 
pressure  gage,  the  chart  of  which  is  moved  always  at  a  speed 
proportional  to  the  speed  of  the  piston.  See  the  author's 
PRACTICAL  HEAT  for  a  discussion  of  the  principle  of  the 
elementary  indicator. 

78.  The    Indicator    Diagram  Is  Extremely  Useful   (D  D, 
Fig.  54)  because  it  enables  one  to  analyze  what  is  taking 

40 


SEC.  79] 


STEAM  ENGINE  INDICATORS 


41 


,51-op 


place  inside  the  engine  cylinder  while  the  engine  is  running. 
There  are,  briefly,  three  ultimate  ends  to  which  such  analyses 
lead: — (1)  They  reveal  whether  the  engine  steam  and  exhaust 
valves  are  opening  and  closing  properly  in  relation  to  the  position 
of  the  engine  piston.  (2)  They  enable  one  to  calculate  the  power 
developed  by  the  expansion  of  the  steam  within  the  engine 
cylinder.  (3)  With  further  cal- 
culations, they  enable  one  to 
determine,  approximately,  the 
amount  of  steam  which  the  engine 
is  using.  Besides  these  three 
important  functions,  the  indi- 
cator diagram  may  reveal  ex- 
traordinary troubles  or  defects 
which  would  otherwise  be  diffi- 
cult to  allocate.  These  uses  of 
the  indicator  diagram  will  be 
considered  separately  in  subse- 
quent sections. 

79.  Watt's  Indicator  Is  Per- 
haps The  Simplest  Form  (Figs. 
54  and  55).  Steam  enters  the 
indicator  cylinder,  C,  from  the 
engine  cylinder,  E.  The  pres- 
sure of  the  steam  forces  the  pis- 
ton P,  upward,  compressing  the 
spring,  S,  and  raising  the  pencil, 
A.  The  sheet  of  paper,  R,  being  moved  at  the  same  time  by 
cord,  F,  which  is  attached  to  the  crosshead  of  the  engine, 
will  have  described  upon  it  a  "diagram,"  DD,  which  indicates, 
at  every  instant  during  a  revolution  of  the  engine,  the  pressure 
within  the  engine  cylinder.  At  any  instant,  the  height  to 
which  the  pencil  has  been  raised  will  be  a  measure  of  the 
pressure  at  that  instant  within  the  engine  cylinder,  whereas 
the  horizontal  distance  through  which  the  paper  has  been 
moved  from  either  end  (for  example,  M,  Fig.  54)  will  denote  the 
position  of  the  piston  in  the  engine  cylinder  at  that  instant. 
From  this  it  follows  that  the  length,  L,  of  the  diagram  repre- 
sents the  length  of  the  engine  piston's  stroke. 


FIG.  54. — External  diagrammatic  view 
of  Watt's  steam-engine  indicator. 


42       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 

NOTE. — MODERN  INDICATORS  (Figs.  53,  56,  and  57)  DIFFER  FROM 
WATT'S  TYPE  only  in  constructional  details.  In  a  modern  indicator  the 
paper,  upon  which  the  diagram  is  traced,  is  held  by  clamps,  K  (Fig.  53) 
to  a  cylindrical  drum,  D,  which  is  given  a  rotative  motion  by  the  cord,  F, 
from  the  engine  crosshead.  Also,  the  pencil,  A,  in  a  modern  indicator  is 
made  to  move  a  distance  greater  than  the  motion  of  the  indicator  piston. 
This  is  accomplished  by  means  of  a  pencil  mechanism.  Then  too,  some 
modern  indicators  have  the  spring,  S,  outside  the  hot  cylinder  (Fig.  57), 
better  adapting  them  for  use  with  superheated  steam. 


FIG.  55. — Sectional  diagrammatic  view        FIG.     56. — Sectional    view    of    a    Thompson 
of  Watt's  steam-engine  indicator.  indicator. 

80.  The  Pencil  Mechanism  (Figs.  58  and  59)  permits  the 
use  of  strong  indicator  springs  (Sec.  92)  which  need  not  be 
compressed  (or  extended)  through  a  great  distance  and  still 
affords  a  diagram  of  reasonable  height.  By  thus  minimizing 
the  extent  of  motion  of  the  heavier  parts,  meanwhile  reducing 
the  weight  of  those  which  have  greater  movement,  modern 
indicators  have  been  made  reasonably  free  from  inertia  effects 
at  the  usual  engine  speeds.  A  good  pencil  mechanism  will 
trace  a  straight  vertical  line  upon  a  card  held  on  the  drum 
(not  in  motion).  It  will  also  cause  the  pencil  to  move  through 
a  distance  exactly  proportional  to  (usually  four  to  five  times) 
the  movement  of  the  indicator  piston. 


SEC.  81] 


STEAM-ENGINE  INDICATORS 


43 


81.  The  Two  Principal  Types  Of  Pencil  Mechanism  Are 
The  "Parallel-Link"  And  "  Curved  -Slot"  mechanisms  (Figs. 
58  and  59).  The  parallel-link  mechanism,  in  some  makes 
of  indicators,  differs  slightly  in  details  from  the  arrangement 
of  Fig.  58  (see  PRACTICAL  HEAT).  In  the  curved-slot 
mechanism  the  roller  on  the  pencil  arm  is  kept  within  the 
slot,  S,  which  is  so  formed  that  the  point  is  given  the  desired 
vertical  motion. 


-Pis  ton  Rod 
Fastened  to 
Spring 


Union 


FIG.  57. — Crosby  outside-spring  indicator  with  reducing  wheel  attached. 

82.  An  Indicator  Reducing  Mechanism  Usually  Called 
A  "Reducing  Motion"  (Fig.  60)  is  necessary  (whenever 
the  stroke  of  the  engine  is  greater  than  the  longest  diagram 
that  can  be  drawn  on  the  indicator  drum)  to  insure  that  the 
full  motion  of  the  engine  piston  may  be  represented  on  the 
indicator  card.  As  the  length  of  diagram  attainable  with 


44       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 


most  indicators  is  from  4  to  6  in.,  it  is  evident  that  nearly  all 
engines  will  require  reducing  mechanisms  of  some  kind. 

NOTE. — Experience  shows  that  for  speeds  over  300  r.p.m.  the  length  of 
diagram  should  not  exceed  3  in.; — speeds  over  200 — 3J^  in.; — speeds 
100  to  200 — 4  in.;  speeds  under  100 — optional. 


Pencil 


I  -  Upper  Position 

Revolving 

Bracket  .--. 


83.  There    Are    Four    Principal 
Types    of    Indicator    Reducing 
Mechanisms.     These  are  the:  (1) 
Pendulum  lever,  Fig.  60.    (2)  Panto- 
graph, Fig.  62  (3)  Reducing  wheel, 
Fig.  66  (4)  Inclined  Plane,  Fig.  69. 
The  first  three  are  the  ones  most 
commonly    used.     Any    of    these 
'•$•'  reducing  mechanisms  can  be  made 
practically  perfect  but,  if  not  care- 
I    fully  set  up,  may  give  results  which 
^  are  very  much  in  error.     Each  type 
will  be  discussed. 


-  Lower  Position 


FIG.  58. — Lever  pencil-mechanism 
for  producing  a  straight  vertical  line. 
(This  is  used  on  Thompson  indicators.) 


FIG.    59. — Curved-slot     parallel     motion     of 
Tabor  indicator. 


84.  The  Pendulum -Lever  Reducing  Mechanism  (Fig.  60) 
is  very  widely  used  and  gives  an  accurate  reduction  if  certain 
requirements  are  observed  in  its  construction.  The  pendulum 
lever,  P,  should  be  at  least  as  long  as  the  engine  stroke  and 
must,  in  its  mid-position,  ab  (Fig.  60),  be  at  right  angles  to 
the  direction  of  motion  of  the  crosshead.  The  connecting 
link,  C,  between  the  pendulum  lever  and  the  crosshead  should 


SEC.  84] 


STEAM-ENGINE  INDICATORS 


45 


be  about  half  the  length  of  the  engine  stroke,  L.  The  pendu- 
lum lever  and  the  connecting  link  must  be  so  arranged  that  the 
point,  m,  where  they  are  fastened  will  be  the  same  distance 
above  the  line  cd  when  the  crosshead  is  at  either  end  of  its 


H 


Ci/K/e  Pulley^ 

/  Engine 
y.  Cylinder-^ 


b  K- -Stroke^- 

FIG.  60. — Pendulum-lever  reducing  motion. 

travel,  as  it  is  below  cd  when  in  mid-stroke.  The  line  cd  is 
a  line,  parallel  to  the  axis  of  the  engine  cylinder,  which  passes 
through  the  center  V  of  the  point  of  attachment  of  the  connect- 
ing link  to  the  crosshead.  Also  the  drum  cord  must  be  led 


FIG.  61. — Inverted  pendulum-lever  with  brumbo  pulley. 

off  at  an  angle  of  90  deg.  to  the  mid-position,  ef,  of  its  lever 
arm.  To  do  this,  it  is  sometimes  necessary  to  enlarge  that 
portion  of  the  lever  as  shown.  Frequently,  a  segment  of  a 


46       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 

grooved  pulley  (Fig.  61)  is  substituted  for  the  pin,  H,  on  the 
pendulum    lever.     This  segment  is  called  a  brumbo  pulley. 

NOTE.  —  THE  PIVOT  POINT,  n,  Is  FREQUENTLY  PLACED  BELOW  THE 
CROSSHEAD  (Fig.  61)  when  it  is  inconvenient  to  provide  a  bearing  for  it 
overhead.  In  such  cases,  the  entire  mechanism  is  simply  inverted  and 
very  often  the  bearing  is  fixed  to  the  floor. 

NOTE.  —  To  FIND  THE  POINT  OP  ATTACHMENT,  H,  (Fig.  60)  or  the 
distance,  Hn,  from  the  pivot  point  to  the  pin  (or  radius  of  brumbo 
pulley),  to  produce  a  certain  length  of  diagram:  RULE.  —  Multiply  the 
total  length  of  the  lever,  mn,  by  the  desired  length  of  indicator  diagram  and 
divide  by  the  stroke  ,L,  of  the  engine,  all  in  inches. 

To  FIND  THE  LENGTH  OF  DIAGRAM  produced  with  the  cord  at  a  certain 
point  of  attachment:  RULE.  —  Multiply  the  distance  from  pilot,  n,  to  point 
of  attachment,  H,  by  the  stroke,  L,  and  divide  by  the  total  length  of  the  lever, 
mn,  all  in  inches. 

EXAMPLE.  —  An  engine  with  a  30-in.  stroke  is  provided  with  a  pendulum 
lever  35  in.  long.  To  obtain  an  indicator  diagram  3  in.  long,  how  far  from 
pivot  must  the  pin  be  placed?  SOLUTION.  —  35  X  3/30  =  3^  in. 

EXAMPLE.  —  An  engine  with  a  24-in.  stroke  has  a  5-ft.  pendulum  lever 
with  a  brumbo  pulley  having  a  radius  of  10  in.  How  long  an  indicator 
diagram  will  it  give?  SOLUTION.  —  10  X  24/60  =  4  in. 

85.  The  Pantograph  Is  An  Instrument  Which  May  Be  Used 
As  A  Reducing  Mechanism  (Figs.  62  and  63)  because  it  con- 
tains two  points  whose  motions  are  always  parallel  and  propor- 
tional to  each  other.  It  may  be  briefly  described  as  a  number 
of  links  pivoted  together  so  that  they  form  two  sets  of  parallel 
links.  One  point,  A,  (Fig.  62  or  63)  is  fixed  stationary. 
Another  point,  J5,  is  given  a  certain  motion,  while  a  third  point, 
C,  will  receive  a  motion  proportional  and  parallel  to  that  of  B. 
Points  A,  B,  and  C  must  originally  be  selected,  however,  on  the 
same  straight  line,  as  shown.  Figs.  64  and  65  show  methods 
of  using  pantographs  on  engines.  Note  that  the  cord  is 
always  taken  from  the  pantograph  in  a  direction  parallel  to  the 
axis  of  the  cylinder. 

NOTE.  —  THE  POSITION  OF  POINT  C  CAN  BE  FOUND  if  the  travel  of  B 
and  the  desired  travel  of  C  (Figs.  62  to  65)  are  known,  by  substituting  in 
this  formula, 

.  travel  of  C  X  distance  AB 

(7)  Dufamo,  AC  =  - 


EXAMPLE.  —  If  Fig.  65  represents  an  engine  whose  stroke  is  24  in.,  and 
an  indicator  diagram  4  in.  long  is  desired,  and  if,  in  the  position  shown  it 


SEC.  85] 


STEAM-ENGINE  INDICATORS 


47 


•  -•  I nd i c a  t  o r  s  -•  -•  ~ 
Engine  Cy  'Under- \ 


FIG.  62. — Simple  pantograph  for  indicator-reducing  purposes. 


FIG.  63. — Adjustable  pantograph  for  indicator-reducing  use. 


Cylinder* 


•Pantograph 
fastened  Here 
C     to  Crosshead 


•Connecting  Rod 


Cord- 


~ '  ~5ta  tionary 
Support 


FIG.  64. — Plan  view  of  an  engine  fitted  with  pantograph  and  indicators. 


48       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 


is  36  in.  from  A  to  B,  what  must  be  the  distance  AC?     SOLUTION. — 
Distance  AC  =  4  X  36/24  =  6  in. 

86.  The    Reducing 


^..-•Engine  Cylinder 

..Indicator      Crosshead., 


Wheel, 

Figs.  66  and  57,  is  a  device  in 
which  a  cord  is  run  directly  from 
the  crosshead  onto  a  pulley 
which  it  rotates,  while  another 
cord  is  run  from  a  second 
pulley  to  the  indicator  drum — 
the  second  pulley  being  either 
smaller  or  geared  to  a  slower 
rotative  speed  than  the  first  and 
driven  directly  from  the  first. 
87.  Features  That  Must  Be  Observed  When  Using  Reduc- 
ing Wheels  are:  (1)  The  wheels  should  be  so  designed  that  under 


FIG.  65.- 


-Elevation  of  an  engine  with  a 
pantograph. 


Indicator 


"' ''Crosshead 


Cord-. 


Pin-' 


FIG.  66. — Principle  of  the  reducing  wheel. 


operating  conditions  the  momentum  of  the  moving  parts  will  not 
become  sufficient  to  produce  slackness  in  the  cord  at  any  time. 


r 


{•-Enq/ine  Fro/me 


.'Core/ 


\    I  -  T  o  p    View 

Reducing  Mot!on-\[ 


I-Top       View 
Reducing  Motion 


incorrect       wrecr    Gu!Je  p,///eyj 
E-S    i    d    e      View  Cock--' 


FIG.  67. — Correct   method  of  connect- 
ing indicator  cord  to  crosshead. 


FIG.  68. — Ifcfrrect  and  corrected 
methods  of  Connecting  indicator  cord 
to  crosshead. 


(2)  A  cord  should  be  used  which  will  not  stretch  to  an\  appreciable 
extent.     Nearly  all  indicator  manufacturers  can  furnish  reduc- 


SEC.  88]  STEAM-ENGINE  INDICATORS  49 

ing  wheels  and  cords  which  will  satisfy  the  above  requirements 
and  which  are  applicable  to  different  types  and  sizes  of  engines. 

CAUTION. — WHEN  USING  REDUCING  WHEELS  always  see  that  the  cord 
(Figs.  67  and  68)  from  the  crosshead  to  the  wheel  is  practically  parallel 
to  the  axis  of  the  engine  cylinder  (K,  Fig.  67)  and  that  the  drum  cord 
leaves  its  pulley  at  right  angles  to  the  axis  of  the  pulley  (R,  Fig.  67). 
This  will  prevent  angular  distortion  of  the  diagram.  Conditions  A  and 
B  (Fig.  68)  besides  causing  distortion  will  tend  to  make  the  cord  run  off 
the  pulleys.  Condition  D  will  give  a  very  poor  reduction  but  may  be 
remedied  either  as  shown  dotted  at  C,  or  as  K,  Fig.  67. 

88.  The   Inclined -Plane   Reducing   Mechanism    (Fig,   69) 
gives  a  very  good  reduction  when  the  angle  through  which  the 
bell-crank,   L,    turns    is   kept 

Dram  Corof-.    ,-Gu/c/e       Crossheacf-^ 

fairly   small.     The   length    of       \         ,,r]  Y      \  .  /   f 

diagram  is  fixed  by  the  incli- 
nation of  the  plane,  P,  and  the 
lengths  of  the  two  arms  of  the 
lever,  L.  The  upright  arm  can 
be  of  such  length  as  to  bring 

the   COrd  in  line  with  the  indi-     FlG-  69.— Inclined-plane  reducing  mech- 

&nism 

cators.     A  catch,  C,  (Fig.  69) 

can  be  arranged  to  hold  the  roller  free  of  the  plane  and  thereby 
stop  the  indicator  without  unhooking  the  cord.  This,  at  the 
same  time,  prevents  flapping  of  the  cord. 

89.  Every  Indicator  Reducing  Motion  Should  Be  Given 
Two  Tests  Before  Using:  (1)  Test  for  accuracy  of  reduction. 
First  divide  the  stroke  of  the  crosshead  into  eight  equal  parts 
(Fig.    70).     Attach    an  indicator,  without  a  spring,  to  the 
cylinder.     Now,  with  the  indicator  attached  to  the  reducing 
motion  and  the  crosshead  at  zero,  make  a  vertical  mark  on  the 
indicator  card  by  raising  the  pencil  lever.     Then  move  the 
crosshead  successively  to  positions  1,  2,  3,  etc.,  making  a 
vertical  mark  on  the  indicator  card  for  each  position.     If  the 
spaces  between  the  lines  on  the  card  are  equal,  the  reduction  is 
satisfactory.     (2)  Test  for  lost  motion  and  inertia  or  momentum 
effects.     Now  run  the  engine  slowly  and  take  an  " atmospheric 
line"   (Sec.   100),  holding  the  pencil  on  during  a  complete 
revolution.     Let  the  engine  get  up  to  speed  and  take  another 
line  about  J-f  g  in.  above  the  first.     A  considerable  difference 


50       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 

in  the  lengths  of  the  two  lines,  indicates  momentum  effects  in 
the  reducing  mechanism  or  the  drum  itself,  or  stretching  of  the 
cord.  The  remedies  are  taking  up  all  lost  motion,  using  a 
short  cord  or  a  wire,  and  so  adjusting  the  drum  spring  that  the 
discrepancy  will  be  a  minimum. 


Scribe  Mark        Scribe  Marks 
on  Crosshead^     on  Ou;de  _ 


It-Mechanism     On      Engine 
FIG.  70. — Method  of  testing  reducing  mechanism  for  accuracy  of  reduction. 

90.  In  Piping  For  Indicators,  great  care  must  be  taken  that 
the  pipe  is  of  sufficient  size  to  allow  the  steam  to  flow  through 
it  without  throttling  (reducing  the  pressure)  and  that  the  pipe 
has  not  sufficient  volume  to  affect  the  working  of  the  engine 
by  increasing  its  clearance  volume. 

NOTE. — THE  BEST  METHOD  OF  PIPING  AN  INDICATOR  is  to  drill  and 
tap  directly  into  the  counterbore  of  the  engine  for  ^-in.  pipe,  as  at  A, 
Fig.  71.  If  the  counterbore  is  too  short  it  is  well  to  chip  a  channel  into 
the  cylinder.  Of  course,  all  chips  must  then  be  removed  from  the 
cylinder  to  prevent  injury  to  it  and  the  indicator.  Where  no  steam  pipes 
or  other  obstructions  appear  at  the  top  of  the  cylinder,  it  is  best  to  locate 
the  indicators  there, — otherwise  they  are  mounted  on  the  side  of  the 
cylinder.  A  straight-way  indicator  cock  (C,  Fig.  71)  is  then  screwed  into 
each  tapped  hole,  preferably  without  any  intermediate  piping.  The  ell 


SEC.  91] 


STEAM-ENGINE  INDICATORS 


51 


shown  below  the  indicator  in  Fig.  65  can  well  be  omitted  so  that  the 
indicator  drum  will  extend  out  horizontally  from  the  cylinder. 

NOTE. — ALL  INDICATOR  COCKS  SHOULD  HAVE  A  RELIEF  PASSAGE 
(X,  Fig.  55)  which  will  relieve  the  pressure  beneath  the  indicator  piston 
when  cock  is  in  the  closed  position. 


Cord 


FIG.  71. — Ideal  method  of  connecting  an  indicator  to  a  cylinder. 

91.  Using  A  Single  Indicator  For  Indicating  A  Cylinder  Is  To 
Be  Avoided,  if  possible,  but  whenever  necessary,  a  three-way 


FIG.  72. — Arrangement  for  using  one  indicator  for  both  ends  of  a  cylinder. 

cock  should  be  used  and  piped  as  shown  in  Fig.  72.     The  indi- 
cator is  thrown  into  communication  with  one  end  of  the 


52       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 


cylinder  and  then  the  other,  giving  the  two  diagrams  on  one 
card.  Diagrams  taken  with  an  indicator  so  arranged  cannot 
be  relied  on  for  accuracy  because  of  the  time  required  to  fill  the 
pipes  with  steam  up  to  the  pressure  within  the  engine  cylinder. 
The  arrangement  of  Fig.  73  is  to  be  especially  avoided,  because 


FIG.  73. — Incorrect  piping  of  an  indicator. 

of  the  excessive  steam  volume  in  the  piping  and  because 
of  errors  due  to  the  two  valves;  if  found  on  an  engine,  this 
arrangement  should  be  replaced.  The  arrangement  of  Fig.  74 
may  be  safely  used  where  it  is  essential  that  provision  be  made 
for  testing  with  either  one  or  two  indicators. 

NOTE. — THE   ARRANGEMENT   OF   FIG.    72    USUALLY    GIVES    POWER 

RESULTS  WHICH  ARE  3  To  7  PER 
CENT.  Too  HIGH,  although  in  certain 
cases  it  gives  results  so  poor  that  it  is 
useless.  It  is  well,  when  using  this 
connection,  to  compare  a  diagram  so 
taken  with  one  taken  with  a  direct 

FIG.  74. —  Piping     arrangement  ,.  ...  .  ,         ,, 

which  is  adaptable  for  either  one  or  connection  and  the  engine  under  the 
two  indicators.  same  load. 

92.  Indicator  Springs  Are  Classified  As  To  Their  Stiffness, 

the  number  (or  scale)  of  an  indicator  spring  being  the  pressure 
(in  pounds  per  square  inch)  which  must  be  exerted  upon  the 
indicator  piston  to  raise  the  pencil  one  inch.  Thus,  a  100-lb. 
spring,  when  in  an  indicator,  would  permit  the  pencil  to  be 
raised  1  in.  by  a  pressure  of  100  Ib.  per  sq.  in.  within  the 


Stop 
Cock 


SEC.  93] 


STEAM-ENGINE  INDICATORS 


53 


engine  cylinder,  2  in.  by  a  pressure  of  200  Ib.  per  sq.  in.  and 
so  on.  Table  93  shows  the  different  springs  made  by  American 
manufacturers  and  the  maximum  safe  pressure  to  which  they 
can  be  subjected,  when  used  with  a  J^-sq.  in.-area  piston. 
When  used  with  a  J^-sq.  in.-area  piston  the  scale  and  safe 
pressure  are  twice  the  values  shown  in  the  table. 


EXAMPLE. — A  50-lb.  spring  when  used  with  a  /^-sq.  in.-area  piston 
becomes  a  100-lb.  spring  with  safe  pressures  of  200  to  240  Ib.  per  sq.  in. 

NOTE. — SINCE  THE  SPRING  Is  THE  ACTUAL  MEASURING  ELEMENT  OF 
AN  INDICATOR,  great  care  must  be  taken  that  it  actually  measures  as  it 
should.  Springs  gradually  change  their  stiffness  with  continued  use  and 
should,  therefore,  be  periodically  tested,  especially  before  and  after  being 
used  on  important  work. 

93.  Table  Showing  Safe  Pressures  For  Indicator  Springs, 

the  higher  values  of  safe  pressure  being  for  engine  speeds 
below  200  r.p.m.;  the  lower  values  for  speeds  up  to  300  r.p.m. 


Scale  of  spring, 
pounds  per  inch 

Safe  pressure, 
pounds  per 
square  inch 

Scale  of  spring, 
pounds  per  inch 

Safe  pressure, 
pounds  per  . 
square  inch 

8 

5  to  10 

60 

120  to  140 

10 

9  to  15 

64 

130  to  145 

12 

11  to  20 

70 

135  to  150 

16 

20  to  30 

72 

140  to  160 

20 

30  to  40 

80 

160  to  170 

24 

40  to  50 

90 

180  to  190 

30 

55  to  65 

100 

200  to  215 

32 

60  to  70 

120 

225  to  240 

40 

80  to  95 

125 

230  to  250 

48 

95  to  115 

150 

265  to  300 

50 

100  to  120 

200 

325  to  380 

94.  In  Testing  An  Indicator  Spring  (Fig.  75),  the  indicator 
should  be  mounted  on  a  vessel,  V,  together  with  a  test  gage,  G, 
and  subjected  to  steam  pressure  in  5-  or  10-lb.  per  sq.  in. 
steps,  beginning  with  atmospheric  pressure  as  zero.  The  cord 
should  be  drawn  by  hand  at  each  pressure  to  obtain  a  hori- 
zontal line  (Fig.  76)  about  half  way  along  the  card.  After  the 
pressure  has  reached  the  maximum  it  should  be  lowered  again 
in  the  same  steps.  The  line  corresponding  to  a  certain  pres- 


54       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 

sure  may  be  higher  now  than  before,  due  to  friction  within 
the  indicator  cylinder.     The  card,  when  the  test  is  completed, 


Indicafor- - 


Outlet-----) 
FIG.  75. — Apparatus  for  testing  indicator  springs  (also  gages  and  thermometers). 

should  look  like  Fig.  76.     The  mean  between  the  two  lines 
drawn  at  a  certain  pressure  is  taken  as  the  average  for  that 


No.  Hour  &??4  K.  __//?    .192  /_  

WKchBnd.—                                i 

Different  Pressures 
at  Which  Spring 

Area 

Length  
HOrd  

Vac.Gage~_^ 

50 

Revs  „ 

ifO 

HE.P  
I.H.R  

%rt^Jf£__.« 

30 

20              * 

20 

\Down 

t       &                I 

L                                   tO 

J  .     :£- 

v* 

Indicator  No. 
1620 

-'-Atmospheric 
Lines 
Observer  •. 

FIG.  76.  —  Sample  card  illustrating  test  of  an  indicator  spring. 

pressure.     The  spring  scale  can  then  be  calculated  from  each 
height  by  substituting  in  the  formula, 


/ON      0     .      0    7 
(8)     Spring  Scale 


pressure,  in  Ib.  per  sq.  in. 
,    .  ,  .  ,    .     .  —  r^- 

height  on  card,  in  inches 


;  ^\."- Atmospheric  • 


SEC.  95]  STEAM-ENGINE  INDICATORS  55 

EXAMPLE. — If  h,  Fig.  76,  is  measured  to  be  1.19  in.,  and  is  the  height 
to  the  50-lb.  line,  as  shown,  then:  spring  scale  =  50/1.19  =  42  Ib.  per  in. 
This  value  supersedes  the  manufacturer's  scale,  which  was  40. 

NOTE. — MANUFACTURERS  WILL  TEST  INDICATOR  SPRINGS,  when  sent 
to  the  factory,  for  those  who  lack  apparatus  for  making  their  own  tests. 
The  author,  however,  recommends  the  construction  and  installation  in 
every  engine  room  of  an  apparatus  similar  to  Fig.  75.  Besides  testing 
indicator  springs,  it  is  very  useful  for  testing  gages  and  thermometers. 
The  indicator  cock  can  readily  be  replaced  by  a  gage  siphon  or  a  ther- 
mometer well.  The  gage  glass  is  unnecessary  except  for  thermometer 
testing,  in  which  tests  water  in  the  glass  insures  saturated  steam. 

95.  In  Selecting  Springs  For  Indicating  An  Engine,  bear  in 
mind  that  the  larger  the  diagram  taken,  the  less  will  be  the 
percentage  error  in  making  cal- 
culations from  it.  There  are, 
however,  certain  limitations  to 
this  policy.  On  high-speed 
engines,  large  diagrams  are  likely 
to  be  accompanied  by  inertia 
effects  in  the  indicator  and  its 

mechanism,    Which   WOUld    intrO-         F™-  77.-Inertia  effects  in  indicator 

diagram  caused  by  too  weak  spring. 

duce    errors    offsetting   the   ad- 
vantages of  the  large  diagrams.     If  too  light  a  spring  has 
been  selected,  these  effects  will  appear  on  the  indicator  diagram 
as  in  Fig.  77,  A  and  B,  and  call  for  a  stiffer  spring. 

NOTE. — IN  GENERAL,  THE  PROPER  SPRING  MAY  BE  SELECTED  IN 
ADVANCE  by  one  of  the  following  rules,  which  are  based  on  a  diagram  not 
over  1%  in.  in  total  height: 

For  non-condensing  engines  (or  cylinders), 

pressure  at  steam  valves 

(9)  spring   scale  =  «%/  (lb.;per  in.) 

For  condensing  engines  (or  cylinders), 

,   vacuum  in  condenser 
pressure  at  steam  valves  H —          — ~ — 

(10)  spring  scale  =   -  • — r-g/ — 

(Ib.  per  in.) 

Wherein:  Pressure  at  steam  valves  is  in  pounds  per  square  inch,  gage. 
Vacuum  in  condenser  is  in  inches  of  mercury  column.  Since  the  vacuum 
in  the  condenser  is  usually  between  25  and  30  in.  of  mercury,  For  (10) 
may  be  simplified  to : 

,,«*  pressure  at  steam  valves  +  15 

(11)  spring  scale  =  ^y  (Ib.  per  in.) 

EXAMPLE. — A   compound   engine   is   operating   under   the   following 


56       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 


.Cap  C.  Not  Held 
in  Finger 


pressures:  Pressure  at  throttle,  200  Ib.  per  sq.  in.  gage.  Pressure  in 
receiver,  4  Ib.  per  sq.  in.  gage.  Vacuum  in  condenser,  27  in.  of  mercury 
column.  Find  spring  scales.  SOLUTION. — Applying  For.  (9)  for  the 
high-pressure  cylinder:  spring  scale  =  pressure  at  steam  valves /!%  = 
200  -5-  1%  =  114?<7  Ib.  per  in.  Hence  a  "  120-lb."  spring  should  be  used. 
Now  applying  For.  (10)  for  the  low-pressure  cylinder:  spring  scale  = 
(pressure  at  steam  valves  +  M  X  vacuum  in  condenser) /!%  =  (4  +  %  X 
27)/l%  =  17.5  -5-  1.75  =  10  Ib.  per  in.  Or  by  applying  For.  (II) -.spring 
scale  =  (pressure  at  steam  valves  +  15)/1%  =  (4  +  15)  -J-  1%  =  19  * 
1.75  =  lO^f  Ib.  per  in.  A  10-  or  12-lb.  spring  might  be  used  here. 

CAUTION. — ALWAYS  USE  A  STIFFER  SPRING  THAN  COMPUTED  rather 
than  a  weaker  spring,  thus  avoiding  the  possibility  of  the  pencil  rising 
above  the  top  of  the  drum  and  catching  there. 

96.  In   Placing   The    Selected    Spring   In   The    Indicator 

one  end  is  fastened  firmly  to  its  stationary  support  (Cap,  C, 
Fig.  56,  in  inside-spring  indicators),  the  other  end  to  the 
piston  (in  some  indicators  to  the  piston  rod).  Before  placing 

the  piston,  spring,  cap,  and 
pencil  mechanism  into  the  indi- 
cator body,  see  that  there  is  no 
excessive  lost  motion  in  the 
parts  (hold  cap  in  one  hand  and 
try  moving  pencil  arm  with  the 
other)  and  adjust  the  pencil  to 
approximately  the  proper  height 
(Fig.  78).  Hold  bracket,  X,  in 
one  hand  and  turn  piston  with 
the  other".  Then  lubricate  the 
indicator  piston,  P,  with  a  drop 
or  two  of  cylinder  oil,  and  the 
f  pencil  mechanism  with  a  very 

light  machine  oil  (manufacturers  supply  porpoise  oil)  and  screw 
cap,  C,  into  place.  If  the  pencil  is  too  high  or  low  repeat  the 
adjustment  until  it  is  correct.  The  pencil  should  be  about  ^ 
in.  above  the  bottom  of  the  card  if  the  indicator  is  used  on  a  non- 
condensing  cylinder.  On  condensing  cylinders  it  must  be  high 
enough  so  that  the  vacuum  on  the  exhaust  stroke  will  not  draw  it 
quite  to  the  bottom  of  the  card. 

EXAMPLE. — On  the  low-pressure  cylinder  of  the  engine  of  the  example 
under  Sec.  95,  the  pencil  should  be  about  l^j  in.  from  the  bottom  of  the 
card. 


FIG.  78. — Method  of  adjusting  pencil 
height. 


SEC.  97] 


STEAM-ENGINE  INDICATORS 


57 


97.  Before  Applying  An  Indicator  To  An  Engine  Always 
Allow  Steam  To  Blow  Through  The  Cock  to  remove  all  dust 
and  grit  that  may  have  settled  there  and  thereby  prevent 
injury  to  the  finely-finished  indicator  cylinder.  It  is  well  to 
have  caps  (Fig.  74)  to  fit  over  the  indicator  cocks  when  they  are 
not  in  use  to  keep  out  foreign  matter.  Then  connect  the  drum 


Center  Line  Of  Inc/tcatorCy/inc/ers "  Wpffi^" "~ 


FIG.  79. — Proper  arrangement  where  two  indicators,  A  and  B,  are  operated  from  one 
reducing  mechanism. 

cords  to  the  reducing  mechanism  as  shown  in  Fig.  79,  and 
adjust  their  lengths  to  get  the  diagrams  in  about  the  centers 
of  the  cards.  Try  the  cord  by  hand  before  attaching  to  the  run- 
ning engine.  Adjust  the  handle  (H,  Fig.  53)  so  that,  when 
pressure  is  applied  to  it,  a  very  light  line  will  be  made  upon  the 
card.  Then  take  pencil  from  drum  and  open  the  cock  to  see 


'Drum 


Paper  Being 
'  Inserted 


Spring 
Clips 


FIG.  80. — Method    of   starting   paper 
on  an  indicator  drum. 


FIG.  81. — Method  of  placing  paper  on  an 
indicator  drum. 


that  the  pencil  will  not  overtravel  the  drum  either  at  the 
top  or  at  the  bottom. 

98.  Indicator  Paper  should  be  smooth,  tough,  and  well- 
calendered,  so  that  it  can  be  handled  without  damage  and 
that  it  offers  little  friction  to  the  passage  of  the  pencil  over  its 


58       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 

surface.  It  should  be  cut  to  the  height  of  the  indicator  drum 
and  about  1  in.  longer  than  the  circumference  of  the  drum. 
The  paper  is  put  on  the  drum  (Fig.  80)  by  inserting  one  corner 
under  the  longer  clip,  bending  the  card  (paper)  around  the 
drum  and  bringing  the  other  corner  under  the  other  clip,  then 
pulling  it  tight  around  the  upper  end  of  the  drum.  Then, 
by  taking  hold  of  the  two  corners  between  the  clips,  the  card  is 
slid  down  the  drum  (Fig.  81),  pulled  tight  again  around  the 
drum  and  the  ends  folded  back.  A  little  practice  enables  one 
to  do  this  quickly  and  neatly. 

99.  The  Indicator  Pencil  should  be  of  hard  lead  and  should 
be  short  and  kept  well  pointed.     Too  long  a  lead  will  cause 
inertia  effects  in  the  pencil  mechanism.     As  the  point  wears 
down,  it  must  be  resharpened  by  rubbing  it  on  a  piece  of  fine 
sand  paper  because  a  fine  line  is  very  essential  in  indicator 
work.     A  metallic  point  can  be  used  on  a  paper  coated  with 
sulphate  of  zinc  and  has  the  advantage  of  keeping  its  point 
although  it  offers  more  friction  than  a  lead  point. 

100.  An  "Atmospheric  Line"  Should  Be  Drawn  On  Each 
Card  before  taking  a  diagram.     It  is  best  drawn  by  holding  the 
pencil  to  the  card  (cock  closed)  and  rotating  the  drum  through 
a  complete  revolution  by  pulling  the  cord  by  hand  as  far  as  it 
will  go,  before  attaching  the  cord  to  the  reducing  mechanism. 
The  importance  of  always  taking  an  atmospheric  line  cannot  be 
overestimated.     Its  uses  will  be  brought  out  in  subsequent 
sections. 

101.  The  Indicator  Diagram  Is  Taken  As  Follows :  (1)  Open 
indicator  cock  and  allow  indicator  to  "warm  up."     (2)  While 
indicator  is  warming  up,  attach  drum  cord  to  reducing  mech- 
anism.    (3)   Hold  pencil  to  paper  for  at  least  three  or  four 
revolutions  of  engine.     (4)  Close  cock  and  unhook  drum  cord. 
(5)  Examine  card  for  evidences  of  indicator  errors.     As  connec- 
tions in  the  indicator  and  at  the  cord  are  apt  to  work  loose,  it  is 
advisable  to  frequently  try  the  indicator  pencil  for  lost  motion 
and  to  watch  that  the  diagram  remains  in  the  center  of  the 
card  (to  make  sure  the  drum  is  not  striking  its  stops). 

NOTE. — CONVENIENT  METHODS  OP  "HooKiNG-Up"  AN  INDICATOR 
CORD  are  illustrated  in  Figs.  82,  83  and  84.  Fig.  85  shows  how  an  adjust- 
able loop  may  be  arranged  in  an  indicator-cord  end.  Fig.  86  illustrates  a 


SEC.  101] 


STEAM-ENGINE  INDICATORS 


59 


[Distance  to  Point 
\  of  Attachment 


Indicator  .........  >• 


,-To  Reducing  Mot/on 
i  .-Wire  Hook 


FIG.  82.  —  Method  of  arranging  drum  cord, 
C,  to  prevent  flapping.  (Connection  is 
effected  by  catching  hook,  H,  in  eye,  E.) 


Wooden 
Pendulum 
Lever 


FIG.  83. — Connection  at  pendu- 
lum lever  to  prevent  flapping  of 
cord.  (Eye,  L,  is  placed  over 
pin,  //.) 


,-lndiccrtor 


Indicator 
Cock. 

•   .-Engine 

j  Cylinder 


FIG.  84. — Convenient  method  of  arranging  an  indicator  cord.  (One  end,  A,  of  the 
cord  is  attached  to  the  indicator  leaving  the  cord  sufficiently  long  that  it  will  not  pull 
taut  when  the  crosshead,  C,  is  in  its  extreme  position.  A  loop,  L,  is  provided  near  the 
indicator  for  "hooking  in.") 


For  fndfcafor  Hook 
Cord 


Ino/i'co/tor  Cord- 
,-To  Indicator 


FIG.  85. — Adjustable  loop  for  indieator- 
cord  end. 


,,-\\-Cord  Bin™ 
\^\When  In     ^ — 
•  •  Position  Shown  uy 
Dotted  Lines 

FIG.  86. — Knot  for  indicator-cord  hook 
whereby  effective  cord-length  can  be 
adjusted  readiJy. 


60       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 


Iron  W/re  • 

Vise  --. 


knot,  for  attaching  the  cord  to  the  hook,whereby  the  cord  length  may  be 
adjusted    readily.     Indicator    cords    should    preferably    be    high-grade, 

smooth  fish  line  known  in  the  trade 
as  "trout  line."  It  should  be  from 
%4  to  %4  in.  in  diameter.  Any 
smooth  cord  which  has  sufficient 
strength  and  which  will  not  stretch 
will  do.  Iron  wire  between  ^£4 
and  ^2  in.  in  diameter,  is  some- 
times used  instead  of  cord  for  opera- 
ting indicators.  No.  22  gage  an- 
nealed iron  wire  or  picture  wire  may 
prove  satisfactory.  Kinks  may  be 
FIG.  87. — Taking  kinks  out  of  No.  22  gage  taken  out  of  iron  indicator  wire  as 


annealed  iron  indicator  wire. 


suggested  in  Fig.  87. 


102.  An  Ideal  Indicator  Diagram  is  shown  in  Fig.  88.  This 
diagram  is  for  an  engine  having  a  stroke  of  32  in.,  cutting  off 
when  the  piston  has  traveled  8  in.  from  the  beginning,  and  the 
exhaust  valve  opening  2  in.  before  the  end  of  the  stroke.  It  is 
assumed  that  the  exhaust  valve  closes  5  in.  before  the  end  of 


5  10  15  20  25  30    32 

Position    of    Piston  in  Cylinder    Cinches  from  End) 

FIG.  88. — Ideal  indicator  diagram  for  a  steam  engine. 

the  return  stroke  and  that  the  steam  valve  opens  when  the 
piston  is  exactly  at  the  end.  The  engine  is  supplied  with 
steam  at  60  Ib.  per  sq.  in.  gage,  and  exhausts  into  a  condenser 
where  the  vacuum  is  12  Ib.  per  sq.  in.  (about  24  in.  mercury 


SEC.  103] 


STEAM-ENGINE  INDICATORS 


61 


column).  A  vertical  scale  of  pressures,  XM,  (Fig.  88)  and  a 
horizontal  scale,  XN,  representing  positions  of  the  piston  are- 
laid  off  on  the  squared  paper.  While  the  piston  travels  its 
first  8  in.,  the  pressure,  LC,  inside  the  cylinder  will,  of  course, 
be  60  Ib.  per  sq.  in.  because  the  steam  valve  is  open.  The 
steam  then  expands  along  a  line,  CR,  until  the  exhaust  valve 
opens  at  R,  where  the  pressure  drops  rapidly,  RE,  to  that  in  the 
condenser.  On  the  return  stroke  of  the  piston  the  pressure, 
EK,  remains  that  of  the  condenser  until  the  exhaust  valve 
closes  (K).  Then  the  steam  which  remains  in  the  cylinder 
is  compressed  (KB)  and  finally,  when  the  piston  reaches  the 
end  of  its  travel,  steam  is  again  admitted  (B)  from  the  boiler 
and  the  pressure  in  the  cylinder  immediately  rises,  BL,  to  the 
pressure  of  the  steam  supply. 

NOTE. — THE  EXACT  FORM  OF  THE  COMPRESSION  AND  EXPANSION 
LINES  depends  upon  the  clearance  volume  and  will  be  treated  separately 
(Sees.  108  and  111). 

103.  The  Actual  Indicator  Diagram  Differs  Widely  From 
The  Theoretical  (except  in  occasional  instances)  for  various 
reasons:  (1)  The  valves  may  not  be  set  to  give  the  best  diagram. 
(2)  The  engine  design  may  not  allow  of  a  perfect  diagram  even 
with  the  valves  in  their  best  setting.  (3)  The  installation  of  the 
engine  may  be  at  fault.'  However,  the  indicator  diagram 
enables  one  to  intelligently  set  the  engine  valves  and  to  know 
why  a  more  perfect  diagram  is, not  obtained.  In  studying 


the    diagram, 
separately. 


each    "line"    of    Fig.    88    will    be  considered 


FIG.    89. — Variations  of  the  admission  line. 

104.  The  "Admission  Line"  Will  Be  Of  Varied  Appearance 
for  different  engines.  BL  (Fig.  88)  and  A,  Fig.  89,  show  the 
ideal  form  in  which  it  often  appears  on  cards  from  slow-speed 
four-valve  engines.  On  high-speed  engines  the  admission  line 


62       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 

(Fig.  90)  is  frequently  lacking  altogether,  a  condition  which  is 
often  satisfactory.  If  the  steam  valve  opens  late  in  the  cycle 
but  still  opens  rapidly,  admission  line  B  (Fig.  89)  will  result. 
With  slow  opening  this  changes  to  the  form  of  C.  Notice, 
here,  that  the  piston  travels  outward  before  the  valve  is  well 
opened,  increasing  in  speed  as  it  progresses,  and  that  the  steam 
does  not  get  a  chance  to  build  up  the  pressure  until  the  piston 
is  well  on  in  its  stroke.  Condition,  D,  occurs  when  the  com- 
pressed steam  in  the  clearance  volume  begins  to  expand  before 
....  f  .  the  steam  valve  opens.  Condition 

InatcaTor  Card---^ 

E  happens  seldom;  here  the  ex- 
haust valve  closes  just  at  the  end 
of  the  return  stroke  and  the  piston, 
moving  outward,  then  expands  the 
steam  in  the  clearance  volume,  re- 
ducing its  pressure  until  the  steam 


\~Posifi6h  of  .Ideal  Admission  Line: 


FIG.  9o.-indicator  diagram  from  valve  opens  allowing  the  pressure 

a  high-speed  engine.     (Showing  ab-     to     build    Up.       Condition    F 


sents    what    happens    to   the   ad- 

mission  line  when  the  steam  valve  opens  at  the  proper  time 
but  the  exhaust  valve  remains  open  too  long.  With  condition 
G,  representing  too-high  compression,  the  opening  of  the  steam 
valve  allows  the  steam  to  flow  out  of  the  cylinder  and  into  the 
steam  chest  until  this  is  again  expanded  by  the  piston  moving 
outward.  Just  as  late  admission,  C,  causes  the  admission  line 
to  slope  away  from  the  end,  so  an  early  admission  causes  it  to 
slope  backward,  as  H  .  In  condition  7,  the  sharp  point  at  the 
top  is  another  indication  of  early  admission.  Decreasing  the 
lead  (see  Divs.  4  and  5)  will  usually  make  the  engine  run  more 
smoothly  and  give  a  rounded  top  as  in  A. 

105.  The  "Steam  Line"  Indicates  The  Pressure  Losses 
(LC,  Fig.  88  and  Fig.  91)  from  the  boiler  to  the  engine 
cylinder  and  depends  on  the  steam-flow  through  all  the 
intermediate  passages. 

EXPLANATION.  —  Just  as  water  will  flow  only  from  a  higher  to  a  lower 
level,  so  will  steam  flow  only  when  there  exists  a  difference  of  pressure 
to  cause  the  flow.  The  greater  the  velocity  of  the  steam  through  the 
passages  and  the  greater  the  internal  surface  area,  in  the  passages,  over 
which  the  steam  must  pass  or  rub,  the  greater,  of  course,  will  be  the 


SEC.  106] 


STEA  M -ENGINE  IN  DIG  A  TORS 


63 


amount  of  frictional  resistance  produced  by  the  steam  passing  through 
the  passages.  The  greater  the  frictional  resistance,  the  greater  again 
must  be  the  difference  of  steam  pressure  to  maintain  the  flow. 

Now,  in  a  steam  engine,  the  steam  is  first  admitted  when  the  piston 
is  about  at  the  end  of  its  stroke  and  moving  very  slowly.  The  volume  to 
be  filled  with  steam  is  only  the  clearance  volume,  which  can  be  filled 
quickly  and  usually  with  a  small  steam  velocity  through  the  ports. 
But  the  velocity  of  the  piston  increases  as  it  moves  toward  mid-stroke 
and  then  decreases  again.  As  the  piston  moves  from  the  end,  steam  must 
rush  in  to  fill  a  rapidly  increasing  volume  and,  the  faster  the  volume 
increases  (piston  travels),  the  more  swiftly  the  steam  must  flow  through 
the  ports.  Thus,  as  the  piston  moves  away  from  the  cylinder  end,  there 
will  be  a  rapidly  increasing  frictional  resistance  in  the  passages — calling, 
in  turn,  for  a  greater  pressure  difference  between  the  boiler  and  cylinder. 

106.  The  Ideal  Steam  Line  (BL,  Fig.  88  and  A,  Fig.  91) 
can  only  be  produced  when  the  velocity  of  the  steam  through 
the  passages  never  becomes  great  enough  to  appreciably 


FIG.  91. — Variations  of  the  steam  line. 

affect  the  frictional  resistance.  This  may  occur  in  a  very  slow- 
speed  engine  with  large  direct  passages.  The  ideal  steam 
line  is  very  nearly  approached  in  most  Corliss  engines.  In 
high-speed  engines,  the  steam  line  looks  more  like  B,  Fig.  91, 
where  the  difference  between  x  and  y  represents  the  additional 
pressure  required  to  force  the  steam  into  the  cylinder  at  the 
higher  velocity  after  the  piston  leaves  the  end.  On  engines 
with  large  steam  chests  the  steam  line  will  appear  more  as 
shown  at  C,  where  the  steam  stored  in  the  chest  is  able  to  keep 
up  the  pressure  in  the  cylinder  until  the  piston  has  moved 
farther  out  in  its  stroke  and  attained  a  higher  velocity. 
Diagram  D  represents  the  total  absence  of  a  steam  line  at 
light  load,  .cut-off  having  taken  place  as  soon  as  the  clearance 
volume  was  filled  with  steam.  Diagram  E  shows  the  varia- 
tion in  pressure-drop  in  a  non-expansive  engine  as  the  speed  of 
the  piston  increases  and  again  decreases  toward  the  end  of  the 


64       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 


stroke.     The  same  sort  of  line  is  usual  where  an  engine  has  a 
very  late  cut-off  point. 

107.  The  Steam-Chest  Diagram  (Fig.  92),  when  combined 
with  the  cylinder  diagrams,  is  very  valuable  for  segregating 
the  pressure  losses  between  the  boiler  and  the  cylinder. 
The  steam-chest  diagram  is  taken  on  an  indicator  which  is 
piped  to  the  steam  chest  and  which  is  driven  from  the  same 
reducing  mechanism  as  that  which  is  used  for  the  cylinder 
diagrams.  The  cylinder  diagrams  are  taken  on  another 
card  (or  combined,  by  tracing  the  diagram  from  one  end  onto 

iz'Steam-Chesf  Card 


^\:V: —;:'•!'•.::  •/•: -.'ijv ':•'•'.  •'•  ^ Boil fr.  Pressure  Line  ':'.',  '  ' 


FIG.  92. — Cylinder  diagrams  superimposed  on  steam-chest  diagram. 

that  from  the  other  end).  The  cylinder  diagrams  and  steam- 
chest  diagram  must  be  taken  with  the  engine  operating  under  like 
conditions.  The  card  with  the  cylinder  diagrams  is  then  cut 
down  in  size  and  pasted  on  the  steam-chest  diagram  with  the 
atmospheric  lines  along  one  line  and  with  the  ends  of  the 
diagrams  above  one  another  as  shown  in  Fig.  92.  The  boiler- 
pressure  line  is  then  drawn  on  the  card  by  hand  at  a  height 
measured  from  the  atmospheric  line  by  the  same  scale  as  that 
of  the  spring  with  which  the  diagrams  were  taken. 

EXPLANATION. — When  the  crank-end  steam  valve  opens  /Fig.  92)  the 
pressure  hi  the  steam  chest  is  reduced.  As  the  piston  moves  away 
from  the  end,  the  pressure  in  the  chest  decreases  as  does  also  the  pressure 
in  the  cylinder.  Up  to  cut-off,  e,  the  drop  between  the  boiler  and  steam 
chest,  be,  and  the  drop  from  the  chest  to  the  cylinder,  cd,  both  increase 


SEC.  108] 


STEAM-ENGINE  INDICATORS 


65 


because  of  the  increasing  velocity  of  the  steam.  After  cut-off,  however, 
steam  is  supplied  from  the  boiler  only  to  fill  the  steam  chest,  and  it  builds 
up  the  pressure  there  rapidly  at  first  (eg)  and  then  more  slowly  (gf)  until 
the  head-end  valve  opens,  again  causing  the  pressure  to  drop.  Sometimes 
the  momentum  of  the  steam  in  the  supply  pipe  causes  the  point  g  to 
appear  much  higher  than  shown.  Line  gf  is  then  practically  parallel  to 
the  boiler-pressure  line. 

NOTE. — DISTANCE  be  CAN  OFTEN  BE  DECREASED  and  the  entire  steam- 
chest  diagram  flattened  out  by  equipping  an  engine  with  a  larger  supply 
pipe.  Likewise,  distance  cd  can  sometimes  be  decreased  by  increasing, 
if  possible,  the  amount  by  which  the  valve  uncovers  the  steam  port. 


r-Inii-'ial  Po/nt 


108.  The  "Expansion  Line"  In  A  Steam  Engine  Usually 
Follows  A  Hyperbolic  Curve  (CR, 
Fig.  88  and  Fig.  93).     That  is,  the 
absolute  pressure  falls  inversely  as 
the  volume  increases.     If  the  vol- 
ume is  doubled,  the  pressure  falls 
to  one  half  the  initial;  when  the 
volume  is  five  times  the  initial,  the    g> 
pressure   is   one   fifth   and   so   on.         vo  urn e-'cu'bSc'  Feet 

Thus,     Fig.     93    represents    the    eX-     FIG.  93.— Hyperbolic  expansion  line 

pansion  of  one  cubic  foot  of  steam  for  steam- 

from  an  initial  pressure  of  60  Ib.  per  sq.  in.  abs.  (about  45  Ib. 

per  sq.  in.  gage). 

EXAMPLE. — Fig.  94  is  an  indicator  diagram  taken  with  a  60-lb.  spring 
from  an  engine  which  has  a  clearance  volume  equal  to  5  per  cent,  of  the 
piston  displacement.  From  the  point  of  cut-off  draw  the  theoretical 
(hyperbolic)  expansion  line. 

SOLUTION. — Since  the  length  of  the  diagram  is  3  in.,  the  clearance 
volume  OA,  can  be  represented  as  5  per  cent  of  3  in.  =  0.05  X  3  =  0.15 
in.,  or  Ko  in.,  and  laid  off  to  the  left  of  the  diagram  as  shown.  The  zero 
pressure  line,  OZ,  can  also  be  laid  off  to  scale  below  the  atmospheric  line 
(15  Ib.  is  near  enough  for  atmospheric  pressure  except  when  spring  scale 
is  very  small).  To  construct  the  theoretical  curve  through  C,  the  point  of 
cutoff,  draw  line  CU,  parallel  to  the  atmospheric  line  and  line  CB 
perpendicular  to  it  and  divide  up  BZ  into  parts  (which  may  be  of  any 
length;  BE,  El,  IM,  MP,  etc.,  as  shown.  Erect  a  perpendicular  at  each 
point  of  division.  Draw  lines  from  the  points  where  these  pendiculars 
cut  the  line  CU  to  point  0  and  note  where  they  cut  CB.  From  the  points 
where  these  diagonal  lines  cut  CB  draw  horizontals  again  to  cut  the 
perpendiculars,  as  FG,  JK,  etc.  The  points  G,  K,  Y,  etc.  will  determine 


66       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 


the  theoretical  expansion  curve  which  can  then  be  drawn  through  them. 
As  is  shown,  it  is  well  to  draw  the  perpendiculars  DE,  HI,  etc.  closer 
together  for  the  first  part  of  the  expansion  curve  than  for  the  end, 
because  the  curve  drops  more  rapidly  at  the  start. 


Zero  Pressure  (Absolute)  Li'ne- 
FIG.  94. — Construction  of  the  theoretical  expansion  line.     (Hyperbolic  curve.) 


109.  The  Expansion  Line  May  Reveal  Leaky  Valves 
(Figs.  95  and  96).  With  valves  properly  seated  (Fig.  92), 
the  actual  expansion  curve  usually  falls  below  the  theoret- 
ical at  the  beginning  and  rises  above  it  toward  the  end. 
A  leaky  exhaust  (or  drip)  valve  may  cause  the  expansion 


...Cut-Off  Point 


Actual  Expansion 


Afmospnenc  LJ -   ~~"-- 
'Zero  'Pressure  Line—-** 


-Cut-Off  Point 

wretical 
<pansion  Line 


\.  ^.Theoretical 
, '  *  N>  x  Cxpansi 


'Actual        ,  „ 
\Cxpansfon  Line 


_ 
---Zero  Pressure  Line 


FIG.    95. — Indicator    diagram    showing 
effect  of  leaky  steam-admission  valve. 


Indicator  Card-— 

FIG.    96. — Indicator   diagram    showing 
effect  of  leaky  exhaust  valve. 


curve  to  lie  exactly  on  the  theoretical  or  below  it,  as  in  Fig.  96. 
A  leaky  steam  valve,  on  the  other  hand,  will  cause  the  expan- 
sion curve  to  lie  well  above  the  theoretical  throughout  its 
length  (Fig.  95). 

NOTE. — Too  MUCH  SHOULD  NOT  BE  INFERRED  FROM  THE  APPEAR- 
ANCE OF  THE  EXPANSION  LINE,  however,  as  there  are  too  many  things 


SEC.  110]  STEAM-ENGINE  INDICATORS  67 

which  might  affect  its  shape.  The  expansion  line  may  follow  the  theoret- 
ical very  closely  in  an  engine  that  has  leaky  steam  and  exhaust  valves. 
Its  study  is  useful  chiefly  in  revealing  general  indications  of  trouble. 

110.  The  "Release"  and  "Exhaust"  Lines  Indicate  How 
Effectively  The  Steam  Is  Taken  From  The  Cylinder  (RE  and 

EK,  Fig.  88w  and  Fig.  97)  .  Since  they  merge  into  one  another 
they  are  difficult  to  study  separately.  The  release  line,  one 
might  say,  begins  at  the  point  of  release,  R,  and  ends  where  the 
pressure  is  decreased  to  its  minimum  value,  as  at  //,  Fig.  97. 
The  exhaust  line  (also  called  the  back-pressure  or  counter- 
pressure  line)  begins  at  H  and  ends  at  K,  the  point  of  com- 
pression, where  the  exhaust  valve  closes.  Since  the  pressure 
in  the  cylinder  during  exhaust  must,  to  produce  a  flow,  be 
more  than  that  into  which  the  cylinder  is  exhausting,  the 
exhaust  line  may  be  expected  lie  above  the  atmospheric 
(when  exhausting  to  the  atmosphere).  If  the  exhaust  pas- 


D  Late  Release  With 
High  Terminal  Pressur 


FIG.  97.  —  Variations  of  release  and  exhaust  lines. 

sages  are  short,  direct,  and  large,  the  pressure  difference  will 
not,  A  and  B,  be  noticeable  on  the  indicator  diagram. 

As  it  is  advisable  to  have  the  pressure,  urging  the  piston 
forward,  decrease  toward  the  end  of  the  stroke,  a  release  line 
as  at  A  is  recommended.  Of  course  the  maximum  of  work 
would  be  obtained  from  the  steam  if  it  were  released  along  the 
line  GH  of  A  but  this  would  result  in  condition  B  in  which  the 
loss  of  work  (shaded)  is  the  same  as  in  A  .  The  mean  between 
these  two  conditions  is  represented  in  C.  With  a  high  ter- 
minal-pressure condition  B  takes  the  shape  of  D,  due  to  the 
inability  of  the  exhausted  steam  to  escape  from  the  cylinder 
because  it  is  expanding  while  the  volume  in  the  cylinder  is 
decreasing.  The  dotted  line  in  D  shows  the  advantage  of  the 
early  release. 

Condition  E  represents  what  may  happen  to  the  exhaust 
line  if  the  exhaust  valve  restricts  the  port  when  it  is  in  its 


68       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 

extreme  position  (too  much  lap);  this  condition  might  also 
appear  in  a  twin-cylinder  engine  where  the  cranks  are  set  at 
90  deg.,  the  hump  being  formed  while  the  other  cylinder  is 
releasing.  If  cut-off  occurs  too  early  in  the  stroke,  the  steam 
may  expand  to  a  pressure  below  exhaust  pressure,  F,  in  which 
case  the  opening  of  the  exhaust  valve  allows  previously 
exhausted  steam  to  flow  back  into  the  cylinder.  As  will  be 
shown  (Sec.  114),  this  over-expansion  represents  a  loss  of  work. 
Over-expansion  can  be  overcome  by  throttling  the  steam  sup- 
ply, thus  causing  a  later  cut-off. 

111.  The  "Compression  Line"  Varies  Widely  In  Different 
Engines  (KB,  Fig.  88  and  Figs.  98  to  100)  depending  on  the 
valve  setting,  condition  of  the  engine,  exhaust  pressure,  and 
the  clearance  volume.  In  general,  it  should  be  the  converse  of 
the  expansion  line,  that  is,  it  should  also  be  a  hyperbolic  curve, 
the  pressure  rising  as  the  volume  within  the  cylinder  is 
decreased.  The  purpose  of  this  increased  pressure  at  the  end 
of  the  stroke  is  primarily  to  aid  in  stopping  the  piston  before 
its  reversal  in  direction  of  travel,  but  by  thus  trapping  some 
steam  in  cylinder,  the  amount  which  must  (when  the  steam 
valve  opens)  be  introduced  to  fill  the  clearance  volume  is 

materially  decreased.  To  com- 
pletely fill  the  clearance  space, 
the  compression  line  would  have 

'tKv*       ^°  ra^se  ^e  Pressure  to  that  of 
^  \p    the    steam    line   as   in   Fig.    90; 
'Conditions  \s\ti,,   since    this  would  be  more 

FIG.  98.— Variations  of  the  compres-    compression    than    is    necessary 

for    stopping    the    piston,    it    is 

recommended  that  there  should  be  just  enough  compression 
to  produce  smooth  running  of  the  engine. 

Usually  this  condition  is  brought  about  when  the  compres- 
sion curve  merges  with  the  admission  line  at  about  %  the 
height  of  the  diagram  (A,  Fig.  98).  In  automatic  engines  the 
compression  depends  upon  the  load  and  at  light  loads  fre- 
quently becomes  excessive  as  at  B.  Condition  C  may  be 
caused  by  the  condensation  of  the  cushion  steam  on  the  cool 
walls  of  the  clearance  space,  but  it  is  more  likely  to  be  the 
result  of  a  leaky  exhaust  or  drip  valve.  Thus  as  the  movement 


.Compression  I  Leaky 
Too  Early    |  Valve 

^Cylinder 
.onclerr- 
,satlon) 


SEC.  112] 


STEAM-ENGINE  INDICATORS 


69 


of  the  piston  becomes  slower  and  the  pressure  higher,  the 
steam  escapes  as  fast  as  the  moving  piston  tends  to  compress 
it.  Condition  D  shows  how,  with  a  leaky  piston,  the  compres- 
sion curve  is  above  the  hyperbolic  (due  to  steam  leaking  in 
from  the  other  end)  up  to  point  a,  where  release  occurs  at  the 
other  end,  falling  then  from  a  to  b,  while  leakage  takes  place 
to  the  other  side  of  the  piston. 

NOTE. — FIG.  99  SHOWS  THE  EFFECT  ON  COMPRESSION  OF  DIFFERENT 
EXHAUST  PRESSURES  in  the  same  engine.  It  is  evident  that  the  pressure 
at  the  end  of  compression  increases  in  direct  proportion  to  the  exhaust 


/'  Per  Cent\  Piston/ Displacement 
'6%  Clearance^         '*Later  Part  of 
Vo/ume  X%     Exhaust  Period 

o%  Compress/on' 
Period 

FIG.  99.— Illustrating  effect  of  exhaust 
pressure  on  compression.  (Compression 
pressure,  for  any  given  engine,  varies 
directly  with  the  exhaust  pressure.) 


Per  Cent  Piston  Displacement 

FIG.  100.  —  Illustrating  effect  of 
different  clearance  volumes  on  the 
compression  curve. 


pressure.  That  is,  if  the  exhaust  pressure  (absolute)  is  doubled  the 
compression  pressure  is  also  doubled,  and  so  on.  Fig.  100  shows  how  the 
compressure  pressure  varies,  with  the  same  setting,  on  engines  with 
different  clearances.  It  is  evident  from  Fig.  100  that  if  the  clearance 
volume  is  equal  to  the  portion  of  the  return  stroke  which  is  uncompleted 
when  the  exhaust  valves  closes,  the  compression  pressure  will  be  twice 
the  absolute  exhaust  pressure.  If  the  clearance  were  but  half  as  great, 
everything  else  remaining  equal,  the  compression  pressure  would  be 
3  times  the  exhaust  pressure.  From  this  it  is  evident  that  in  engines 
with  very  small  clearance  volumes  the  exhaust  valve  must  close  late  in 
the  stroke  or  a  high  compression  pressure  will  result. 

112.  Examples   Of  Indicator  Diagrams  Revealing  Faults 

are  included  here  to  better  familiarize  the  reader  with  their 


70       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 


analysis.  Methods  of  correcting  faulty  valve-settings  will  be 
discussed  in  Divs.  4  and  5.  Methods  of  correcting  mechan- 
ical faults  will  be  treated  in  Div.  13. 

EXAMPLE. — Fig.  101  is  a  card  taken  from  a  simple,  high-speed  engine. 
The  sloping  admission  lines  at  a  and  c  show  late  admission.  Cut-off 
in  the  head  end  at  6  shows  a  lower  pressure  than  in  the  crank  end  at  d. 
This,  together  with  the  earlier  cut-off  at  6,  indicates  that  the  port  is  not 
well  uncovered  at  the  head  end  to  allow  the  steam  to  enter.  Although 


'.--Atmospheric  Line 


Atmospheric  Line-^. 


FIG.    101. — Example   of   faulty   indicator 
diagrams  from  a  simple  engine. 


FIG.    102. — Example  of  faulty   indicator 
diagrams  from  a  simple  Corliss  engine. 


release,  r,  is  not  too  late,  it  could  well  be  advanced  a  little.  At  /  the 
uncompleted  portion  of  the  return  stroke  is  about  twice  that  at  g. 
Although  g  occurs  too  early,  /  is  even  worse  in  this  respect.  This  may 
account  for  the  curving-off  of  the  compression  line  at  e  due  to  cylinder 
condensation  at  the  high  pressure. 

EXAMPLE. — Fig.  102  is  a  card  taken  from  a  simple  Corliss  engine.  Late 
admission  is  again  shown  at  a  and  b.  The  sloping  steam  line  toward  c 
shows  only  partial  valve  opening.  Late  release  is  shown  at  e  and  /. 
Compression  takes  place  a  little  late  at  g,  whereas  it  is  satisfactory  at  h. 

EXAMPLE. — Fig.  103  shows  diagrams 
which  are  satisfactory  except  for  the 
compression  curve  at  a.  An  effort 
has  been  made  here  to  obtain 
compression  by  closing  the  exhaust 
valve  early  in  the  return  stroke  but 
the  steam  leaks  out  as  the  pressure  is 
raised.  Since  the  pressure  at  a  is  less 
than  at  c,  the  leak  is  not  at  the 
piston  and  must  be  at  the  exhaust  valve  or  drain  cock. 

113.  In  Determining  The  Horse  Power  Or  Steam  Consump- 
tion Of  An  Engine  The  "Mean  Effective  Pressure"  Must  Be 
Known,  for  reasons  which  will  be  explained.     But  first  the 
methods  of  finding  mean  effective  pressure  will  be  discussed. 

114.  In  Finding  The   Mean  Effective   Pressure  By  The 
Method  Of  Ordinates  (Figs.  104  to  106)  the  length  of  the  dia- 
gram is  divided  into  ten  equal  parts  and  perpendiculars  are 


^^Atmospheric   Line 


FIG.  103.- 


-Indicator  card  from  a  simple 
Corliss  engine. 


SEC.  114] 


STEAM-ENGINE  INDICATORS 


71 


erected  at  the  middle  point  of  each  division.  The  length  of 
each  perpendicular  is  measured  or  the  pressure  which  it  repre- 
sents is  found  by  a  scale  corresponding  to  the  spring  number. 
The  average  height  or  average  pressure  is  then  found  as 
explained  below.  The  use  of  lengths  is  better  than  that  of 


Diameter     24- 
Stroke         46* 
Revolutions    10 
Spring  Scale  50 


Indicator  Card  -^ 
FIG.   104. — Finding  Pm  by  the  method  of  ordinates. 

pressures  because  it  permits  of  correction  for  the  true  spring 
scale  (Sec.  94). 

EXAMPLE. — Fig.  104  illustrates  the  method  of  measuring  the  pressure 
along  each  perpendicular.  (Scales  to  correspond  to  those  of  indicator 
springs  can  be  had  from  indicator  manufacturers.)  The'  length  of  each 
perpendicular  is  measured  and  written 
at  its  foot;  for  example,  with  a  50 
scale,  the  length  of  ab  is  87.  The  ten 
pressures  are  then  added  and  the  sum 
divided  by  ten.  The  result  is  the 
"mean  effective  pressure"  which  in 
Fig.  104  is  42.45  Ib.  per  sq.  in. 

NOTE. — A  CONVENIENT  WAY  To 
ERECT  THE  TEN  PERPENDICULARS 
(Fig.  105)  is  to  first  draw  vertical 
lines  AC  and  BD  at  the  ends  of  the 

diagram,  then  lay  a  ruler  with  the  zero  and  5-in.  marks  on  these  lines  and 
place  a  dot  at  each  ^-  and  %-inch  mark  as  shown,  and  later  erect 
perpendiculars  through  each  dot  as  indicated. 

EXAMPLE. — Fig.  106  shows  a  convenient  method  of  adding  the  lengths 
of  the  perpendiculars  on  the  edge  of  a  strip  of  paper.  The  paper  is  placed 
in  position  7,  with  its  edge  along  the  first  perpendicular  and  with  its 


Fig.  105. — Locating  mid-points  for  find- 
ing Pm  by  the  method  of  ordinates. 


72       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 


corner  at  the  lower  end  of  the  perpendicular,  and  a  mark,  1,  is  made  on 
the  paper  at  the  upper  end  of  the  perpendicular.  This  mark  is  then 
placed  (Position  II)  at  the  lower  end  of  the  second  perpendicular  and 
mark  2  is  made  at  the  upper  end.  This  is  continued  until  the  ten 


1 

j^-'Paper  Strip 

•.'[Penciled-  in'.-' 
.  •  Ordinates^  •    '  ( 

'"Pencil 
Mark 

^ 

S| 

\ 

^j.'- 

-'•-.'•'.        •;.'•'•  •.  £• 

indicator 
Diagram- 


-Atmof- 
phenc 
Line 


V 

2 

<--  -Paper 
Strip 

*"*? 

1 

1 

\ 

N 

i 
u 

-Second 

Position 

I-  First.  Position 


FIG.  106. — Adding  lengths  of  perpendiculars  on  a  paper  strip. 

perpendiculars  have  been  laid  off.  The  length  of  the  strip  of  paper  from 
its  end  to  mark  10  is  then  the  sum  of  the  lengths  of  the  perpendiculars, 
which  can  be  divided  by  10  to  get  the  average  length.  The  average 


--Indicator  Diagram 


III!  ~\  T 
Heights  Of  Perpendiculars-"'' 


Ind/cator  Card-....^( 
FIG.   107. — Finding  Pm,  when  over-expansion  takes  place,  by  the  method  of  ordinates. 

length   multiplied  by  the  "true  scale"  of  the  indicator  spring  gives  the 
mean  effective  pressure. 

NOTE. — IN  CASES  OF  OVER-EXPANSION  (Fig.  107)  after  point  a  is 
passed,  the  forward  pressure  on  the  piston  is  less  than  the  back  pressure 


SEC.  115] 


STEAM-ENGINE  INDICATORS 


73 


on  the  return  stroke.  This  means  that,  instead  of  being  forced  forward 
by  the  steam,  the  piston  is  actually  doing  work  on  the  steam  in  expanding 
it.  The  loop,  therefore,  represents  work  lost  during  that  portion  of  the 
stroke.  Hence  the  pressures  of  the  loop  must  be  subtracted  from  those 
of  the  main  portion.  Adding  ordinate  pressures  for  Fig.  107,  the  sum 
of  the  pressures  in  the  main  portion  =  97  +  93+41+20  +  6  =  257  Ib. 
per  sq.  in.  The  sum  of  the  pressures  in  the  loop  =  3  +  9  +  13  +  15  + 
12  =  52  Ib.  per  sq.  in.  The  difference  =  257  -  52  =  205  Ib.  per  sq.  in. 
Then  the  average  or  mean  effective  pressure  =  205  -5-  10  =  20.5  Ib.  per 
sq.  in. 

115.  The  Planimeter  Affords  A  More  Accurate  Means  For 
Finding  The  Mean  Effective  Pressure  than  does  the  method  of 


FIG.   108. 


Amsler  polar  planimeter  and  its  correct  use  in  finding  areas  of  indicator 
diagrams. 


ordinates.  Generally  speaking,  a  planimeter  is  an  instrument 
for  finding  the  area  of  any  closed  figure.  In  some  of  its  forms 
it  enables  one  to  find  directly  the  average  height  of  an  indi- 
cator diagram  or  even  the  mean  effective  pressure. 

116.  The  Amsler  Polar  Planimeter  (Fig.  108)  is  one  of  the 
most  simple  and  enables  one  to  find  the  area  enclosed  by  the 
indicator  diagram  by  guiding  the  tracer  point,  T,  around 
the  diagram  in  a  clockwise  direction.  The  planimeter  measures 
the  area  in  square  inches. 

OPERATION.  —  The  indicator  card  should  be  fastened  with  thumb  tacks 
to  a  smooth  board  and  on  a  piece  of  drawing  paper  or  Bristol  board  which 


74       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 

is  large  enough  to  include  the  card  and  the  planimeter  in  every  position  it 
will  take.  The  fixed  point,  P,  should  be  so  placed  that  the  planimeter 
arms  will  not  be  closed  when  T  is  nearest  to  P  and  that  the  arms  will  not 
open  too  nearly  into  a  straight  line  when  in  their  maximum  position 
(Fig.  108  shows  a  good  position).  The  point,  T,  is  then  placed  at  some 
point  on  the  diagram  and  a  slight  pressure  applied  to  it  so  as  to  make  a 
depression  in  the  card  at  that  point.  The  reading  of  the  wheel,  W,  and 
the  vernier  is  then  recorded.  The  point,  T,  is  then  guided  carefully 
around  the  diagram  in  the  clockwise  direction,  as  shown,  until  the 
depression  is  again  reached.  Another  reading  of  the  wheel  and  vernier  is 
taken.  The  difference  between  the  two  readings  will  be  the  area  of  the 
diagram.  The  length  of  the  diagram  is  then  measured  between  perpen- 
diculars erected  at  the  ends  (AC  and  BD,  Fig.  105).  The  area  of  the 
diagram  divided  by  its  length  gives  its  mean  height.  The  product  of  the 
mean  height  and  the  true  scale  of  the  indicator  spring  is  the  mean  effective 
pressure. 


FIG.   109.  —  Diagrammatic   illustration   of   polar  planimeter   with   adjustable   arm  for 
finding  mean  height  of  indicator  diagrams. 

NOTE.  —  WHENEVER  THE  DIAGRAM  Is  So  Low  ON  THE  CARD  THAT  THE 
WHEEL  MIGHT  CROSS  THE  EDGE  OF  THE  CARD,  the  card  should  be 
inverted  into  the  position  shown  dotted  in  Fig.  108. 

EXAMPLE.  —  An  indicator  diagram,  taken  with  a  60-lb.  spring,  is  found 
by  planimetering  to  have  area  of  1.05  sq.  in.  and  is  3>£  in.  long.  What 
is  the  mean  effective  pressure?  SOLUTION.  —  Mean  effective  pressure  = 
(1.05  -T-  3>^)  X  60  =  20  Ib.  per  sq.  in. 


117.  Polar  Planimeters  With  Adjustable  Tracer  Arms 
(Fig.  109)  are  averaging  planimeters;  that  is  they  have  the 
advantage  that  they  will  measure  the  average  or  mean  height 
of  a  diagram  directly  on  the  wheel  arid  vernier  (usually  in 
fortieths  of  an  inch).  To  accomplish  this  the  tracer  arm,  A, 


SEC.  118] 


STEAM-ENGINE  INDICATORS 


75 


Indicator  Card- 


which  slides  in  or  out  through  H,  must  be  so  set  that  the  dis- 
tance between  M  and  N  is  equal  to  the  length  of  the  indicator 
diagram. 

118.  The  Coffin  Planimeter  Is  Also  An  Averaging  Instru- 
ment (Fig.  110).  The  indicator 
diagram  is  placed  with  its  atmos- 
pheric line  along  the  horizontal 
clip,  K,  and  ends  almost  touching 
the  fixed  and  movable  vertical 
clips,  F  and  S.  It  is  then  plani- 
metered  as  with  the  Amsler 
planimeter.  If  the  start  and 
finish  point  is  selected  at  the  ex- 
treme right  of  the  diagram  (G, 
Fig.  110),  the  final  reading  of  the 
wheel  and  vernier  need  not  be 
taken.  The  tracer  point  can  be 
moved  up  vertically  along  the 
movable  clip,  S}  with  the  operator 
keeping  his  eye  on  the  vernier 
until  the  reading  of  the  wheel  is 

the  same  as  before  tracing  the  diagram.  Assume  that  this 
condition  obtains  when  the  tracer  point  reaches  H.  Then  the 
height,  GH,  is  the  mean  height  of  the  diagram.  If  the  scale, 

Drawing 


-Groove "^Smooth   Brlsfol  Board 
M       Surface  For  Wheel  To 
a!Ho  nn 


Ride  On 


(Ash~ 


FIG.   111. — Willis  planimeter  with  adjustable  tracer  arm.     (Jas.  L.  Robertson  and  Sons.) 

S,  which  forms  the  moving  clip,  is  the  same  as  the  number  of 
the  spring,  and  if  its  zero  be  set  at  G,  the  mean  effective  pres- 
sure, in  pounds  per  square  inch  can  be  read  off  directly  at  H. 


76       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 

119.  The  Willis  Planimeter  (Fig.  Ill)  has  a  wheel,  W  ,  which 
moves  longitudinally  along  its  axis,  XY,  a  distance  propor- 
tional to  the  area  circumscribed  by  its  tracer  point,  T.     The 
movement  of  the  wheel  will  give  the  mean  effective  pressure 
directly,  if  the  length  of  the  tracer  arm,  A,  is  equal  to  the 
length  of  the  diagram,  and  if  scale,  S,  is  of  the  same  number  as 
that  of  the  indicator  spring. 

120.  In  Computing  Horse  Power  From  Indicator  Diagrams, 
there  are  briefly  four  steps:  (1)  Find  the  horse  power  constants, 
k,  for  1  Ib.  mean  effective  pressure  and  1  r.p.m.,  for  each  end  of 
each  cylinder.     (2)  Find  the  mean  effective  pressures  from  indi- 
cator cards,  for  each  end  again.     (3)  Find  horse  power  for  each 
end.     (4)  Find  total  horse  power  of  engine. 

The  theory  of  the  computation  of  indicated  horse  power 
from  indicator  diagrams  is  treated  in  Sec.  18.  As  developed 
there  : 

(12)  Pihp  =     m/aP  (horse  power) 


Wherein  :  —  Pihp  =  indicated  horse  power  developed  in  one  end 
of  the  cylinder.  Pm  =  mean  effective  pressure,  in  pounds 
per  square  inch.  LJS  =  length  of  stroke,  in  feet.  Aip  =  area 
of  piston,  exclusive  of  rod,  if  rod  extends  through  the  head,  in 
square  inches.  N  =  speed  of  engine  shaft,  in  revolutions  per 
minute. 

121.  The  Horse-Power  Constant,  k,  is  made  up  of  the  terms 
that  cannot  change  in  For.  (12).  These  are  evidently  L/s, 
Aip,  and  the  denominator  (33,000).  Pm  and  N  will  depend 
upon  operating  conditions  —  load,  steam  pressure,  etc.  If  the 
latter  are  each  taken  equal  to  one,  For.  (12)  becomes 

(13)  Pihp  =    <  =  k       (horse  power  constant) 


Wherein  :  k  is  the  horse  power  constant  for  a  certain  end  of  an 
engine  cylinder  =  h.p.  for  1  Ib.  mean  effective  pressure  and 
1  r.p.m. 

EXAMPLE.  —  An  engine  has  a  stroke  of  30  in.,  a  piston  18  in.  in  diameter, 
and  a  2%  in.  diam.  piston  rod.  What  are  its  horse  power  constants? 
SOLUTION.—  For  head  end  of  cylinder:  Aip  =  18  X  18  X  0.7854  = 
254.5  sq.  in.;  L/s  =  2.5  ft.;  k  =  2.5  X  254.5/33,000  =  0.0193  =  1/51.8. 


SEC.  122]  STEAM-ENGINE  INDICATORS  77 

For  crank  end  of  cylinder:    AiP  =  254.5  —  (area  of  piston  rod)  =  254.5  — 
3.547  =  251    sq.    in.;    k2  =  2.5  X  251/33,000  =  0.019  =  1/52.6. 

NOTE. — To  avoid  the  use  of  decimal  fractions,  it  is  convenient  to  use 
the  horse  power  constant  expressed  as  a  fraction  whose  numerator  is  one. 

122.  Methods  Of  Finding  The  Mean  Effective  Pressure, 
Pm,  Have  Already  Been  Given,  Sees.  114  to  119.     It  may  be 
well  here  to  lay  down  two  rules  for  use  when  Pm  is  not  found 
directly. 

(14)  P.- 

area  of  diagram  in  sq.  in.  X  scale  of  spring  in  Ib.  per  in. 
length  of  diagram  in  inches 

(Ib.  per  sq.  in.) 
Or: 

(15)  Pm  = 

mean  height  of  diagram  in  in.  X  scale  of  spring  in  Ib.  per  in. 

(Ib.  per  sq.  in.) 

123.  To  Find  The  Horse  Power  For  Each  End  Of  One 
Cylinder  one  needs  only  to  multiply  the  horse  power  constant 
by  the  mean  effective  pressure  for  that  end  and  by  the  speed. 

Or: 

(16)  Pihp  =  PmNk  (horse  power) 

EXAMPLE. — In  the  engine  of  the  example  of  Sec.  121,  if  Pm  for  the  head 
end  were  49  Ib.  per  sq.  in.,  for  the  crank  end  53  Ib.  per  sq.  in.,  and  if 
N  =  105  r.p.m.,  what  horse  power  is  developed  in  each  end?  SOLU- 
TION.— For  head  end,  substituting  in  For.  (16),  Pihp  =  PmNki  =  49  X 
105  X  0.0193  or  49  X  105  -f-  51.8  =  99.3  h.p.  For  crank  end,  Pihp  = 
P'm  N  X  &2  =  53  X  105  X  0.019  or  53  X  105  -J-  52.6  =  105.8  h.p. 

124.  The  Horse  Power  As  Computed  From  The  Indicator 
Diagrams  Is  Called  The  Indicated  Horse  Power  and  repre- 
sents the  power  actually  developed  by  the  steam  within  the 
engine  cylinder  (Sec.  11).     Since  some  portion  of  this  power  is 
lost  by  friction  within  the  engine,  as  at  the  several  bearings  and 
sliding  members,  all  of  it  cannot  be  realized  from  the  engines 
for  further  work. 

125.  "Friction  Horse  Power"  Is  That  Part  Of  The  Indi- 
cated Horse  Power  Which  Is  Lost  Within  The  Engine  Itself 


78       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 

(Sec.  11).  With  a  given  engine,  the  magnitude  of  the  friction 
horse  power  depends  upon  the  load  and  the  steam  pressure  but 
changes  only  slightly  under  the  varying  conditions.  If  the 
engine  is  unbelted  or  uncoupled  from  all  its  load,  then  all  the 
power  developed  by  the  steam  (indicated  horse  power) 
becomes  friction  horse  power. 

126.  The  Brake  Horse  Power  Is  The  Power  That  The 
Engine  Delivers,  at  its  shaft,  or  pulley  to  some  other  machine 
(Sec.    11).     It  is,   of   course,   less  than  the  indicated  horse 
power  by  the  -amount  of  the  friction  horse  power.     Where  an 
engine  is  driving  an  electric  generator  the  efficiency  of  which  is 
known  (and  in  certain  other  cases,  see  Div.   12)  the  brake 
horse  power  can  be  determined  separately. 

127.  The  Brake  Horse  Power  Is  Computed  From  Indicator 
Diagrams,  indirectly,  whenever  it  cannot  otherwise  be  found; 
see  Div.  12.     Thus,  the  indicated  horse  power  may  be  com- 
puted from   the  indicator  diagrams  directly.     Then  if  the 
friction  horse  power  is  subtracted  from  the  indicated  horse 
power,     the    brake    horse    power    will    result.     That    is — 

(17)     Brake  h.p.  = 

Indicated  h.p.  —  Friction  h.p.     (horse  power) 

NOTE. — MANUFACTURERS  OF  ENGINES  WHICH  ARE  TESTED  BEFORE 
LEAVING  THE  FACTORY  CAN  GIVE  THE  FRICTION  HORSE  POWER  OF 
THEIR  ENGINES  AT  DIFFERENT  LOADS.  This  information  is  often  very 
valuable  when  tests  are  to  be  made  or  performance  guarantees  verified. 

128.  The  Weight  Of  Steam  Used  By  An  Engine  Can  Be 
Computed  from  the  volume  of  the  cylinder,  the  number  of 
times  it  is  filled  in  a  certain  time  and  the  weight  of  a  unit 
volume  of  steam  at  the  pressure  at  which  the  cylinder  is  filled. 
If  steam  were  a  perfect  gas  (see  PRACTICAL  HEAT)  or  a  liquid, 
and  if  there  were  no  leakage  either  at  the  piston  or  the  valves, 
such   a   computation   would   be   reasonably   accurate.     But, 
since  steam  is  a  vapor  continually  changing  in  the  engine 
cylinder  (some  of  it)  either  from  the  liquid  to  the  vapor  or 
from  the  vapor  to  the  liquid  state,  and,  since  leakage  is  quite 
common,  the  calculated  weight  of  steam  used  is  never  equal 
to  the  actual,  being  usually  less  because  the  steam  is  partially 
condensed   inside   the   cylinder.     The   calculation   is   of   use, 


SEC.  129]  STEAM-ENGINE  INDICATORS  79 

however,  for  comparison  purposes  and  as  a  measure  of  the 
ideal  minimum  amount  of  steam  which  could  be  used  by  an 
engine  under  the  conditions. 

129.  The  Weight  Of  Steam  Used  By  An  Engine  With  No 
Clearance  (Fig.  112)  can  be  found  by  the  following  formula,  the 
derivation  appearing  below: 

/ION  TIT-          13,750  D'psxs 

(18)  Wih  =        —5—  (Ib.  per  i.h.p.hr.) 

*  m 

Wherein:  W,-*  =  weight  of  steam  used  by  one  end  of  an 
engine,  in  pounds  per  indicated  horse  power  hour.  D'ps  = 
density  of  steam  at  a  selected  point  on  the  expansion  line  , 
in  pounds  per  cubic  foot.  xs  =  fraction  of  stroke  completed 
(Fig.  112)  at  that  point.  Pm  =  mean  effective  pressure,  in 
pounds  per  square  inch. 

DERIVATION.  —  The  volume  of  the  cylinder  is  A.pL/,/144  cu.  ft.  (A,-p  = 
area  of  piston  in  square  inches.  L/s 

=  length  of  stroke  in  feet.)  It  is  |  ^.Cuf-off  Point 
filled  N  (r.p.m.)  times  per  minute  or 
60  N  times  per  hour.  The  total  vol- 
ume to  be  filled  per  hour  is  then  60 
NAifLft/144;  cu.  ft.  If  release  occurs 
at  d,  the  end  of  the  stroke,  where  the 
pressure  is  Pa  and  the  density  is  Dps 
Ib.  per  cu.  ft.,  the  weight  of  steam 
used  per  hour  is  then  60  NAipLfSDps/l4:4: 

Ib.  As  the  engineer  usually  wants  to  FlG-  112-—  Theoretical  diagram  from 
i  ,r  •  r  ,  /•  an  engine  with  no  clearance. 

know    the   weight  of   steam  used  per 

indicated  horse  power  per  hour  (W,-*)  and  as  the  indicated  horse  power 
of  the  engine  is  by  For.  (12)  PmLf&AipN/33,OOQ,  it  follows  that: 
W         weight  used  per  hour  _  60  NAipLfsDps/l4:4 
horse  power  ~  PmLfsAipN/  33^000 

60  NAipLfsDp,  33,000       13,750  Dpi     /1U 

~~    (lb-  per  1-h-p-  hr-} 


Since  at  any  other  point,  6  (Fig.  112),  after  cut-off,  the  weight  of  steam 
within  the  engine  cylinder  must  be  the  same  as  at  d,  it  would  be  possible 
to  go  through  the  same  reasoning  for  any  point  and  get  the  same  result. 
The  volume  filled  each  stroke  would  be  only  a  fraction,  xs  (Fig.  112)  of 
the  total;  but  the  pressure  being  P'0,  the  density  would  be  D'ps.  We 
would  get: 
(20)  Wih  =  i?,750  D^x.  Qb  ^  .^  ^  } 

*•   m 

which  is  the  same  as  For.  (18). 

NOTE.  —  Wih  is  computed  separately  for  each  end  of  the  cylinder. 


80       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  3 


130.  The  Weight  Of  Steam  Used  By  Any  Simple  Engine 
Can  Be  Computed  From  The  Indicator  Diagrams  by  the 

following  formula,  the  derivation  of  which  follows  : 


(21) 


xc)D'pa  - 


(lb.  per  i.h.p.  hr.) 

Wherein  :  xc  =  clearance  volume  expressed  as  a  fraction  of  the 
piston  displacement.  x'a  =  fraction  of  return  stroke  uncom- 
pleted at  a  chosen  point  on  the  compression  curve.  D"ps  = 
density  of  steam  at  that  point  in  pounds  per  cubic  foot.  The 
other  symbols  the  same  as  in  For.  (18). 


Scale  of  Spring  =  40 
Pm  =  47.5  Lb.  Per  Sq.  In. 


**•$ 

i  C j. 

T4^^^lf.- Compression  Point 

k-— (y-K— -  r:74* — j- -? 

Pa=/PLfe  AT5?.//*  ^eroPressureLfne          j 


Sq.  In 


Indicator 

Fia.  113.  —  Indicator  diagram  from  a  simple  engine.     (Calculation  of  steam 
consumption.) 

DERIVATION.  —  Referring  to  Fig.  113,  the  diagram  being  from  an  engine 
having  a  clearance  volume  of  5  per  cent,  of  the  piston  displacement,  the 
volume  in  the  cylinder  at  6  is  (x,  +  xc}AipLfS/l44.  Proceeding  as  in  the 
preceding  section  the  result  would  be,  if  this  volume  were  filled  every 
revolution  — 

w,u  .  IMSOJJ^         (grosS;  lb.  per  i.h.p.  hr0 


(22) 


But,  since  some  steam  is  trapped  in  the  cylinder  at  k,  when  the  exhaust 
valve  closes,  all  the  steam  necessary  to  fill  the  volume  at  6  and  at  a 
pressure  P'a  will  not  have  been  admitted  every  revolution.  It  is  possible 
likewise  to  find  the  weight  not  rejected  by  taking  some  point,  /,  on  the 
compression  line  and  applying  to  it  the  same  reasoning.  The  result 
would  be: 


(23) 


W" 


(unrejected,  lh    per  i.h.p.  hr.) 


Wherein:  x'8  =  uncompleted  fraction  of  stroke  at/.     D"ps  =  density  of 


SEC.  131]  STEAM-ENGINE  INDICATORS  81 

steam  at  /,  in  pounds  per  cubic  foot.     The  net  weight  of  steam  required 
will,  of  course,  be  the  difference  between  W'i/,  and  W"a,  which  is 

n±\  w     -W          w-          13.750  P'P.Qc.+s«)       13,750  P",.(s'.+se) 

\£^j    Wi/i  —  w  ih        vv   ih  —  -p  ^ 

*  m  *  m 

=  ^^  \(xs  +  xc)D'ps  -  (x's  +  xc)D"ps]        (Ib.  per  i.h.p.  hr.) 

"m         L  J 

which  is  the  same  as  For.  (21). 

NOTE. — THE  POINTS,  6  AND  /,  ARE  BEST  CHOSEN  NEAR  THE  LOWER 
ENDS  of  their  respective  lines,  because  there  the  quality  of  the  steam 
is  apt  to  be  highest  (during  expansion,  the  quality  increases;  during 
compression,  it  decreases)  and  errors  due  to  moisture  in  the  steam  will  be 
minimized. 

EXAMPLE. — Fig.  113  represents  a  diagram,  showing,  with  a  40-lb. 
spring,  a  mean  effective  pressure  of  47.5  Ib.  per  sq.  in.  How  much  steam 
is  accounted  for  by  the  diagram?  SOLUTION. — The  whole  length  of  the 
diagram  is  4  in.  xs  =  3.5  in./4  in.  =  0.875.  xc  =  5  per  cent.  =  0.05. 
x's  =  0.4  in. /4  in.  =  0.10.  P'«  =  32  Ib.  per  sq.  in.  abs:  andP"0  =  19  Ib. 
per  sq.  in.  abs.  From  steam  tables,  D'ps  =  0.077,3  and  D"pi  =  0.047,46 
Ib.  per  cu.  ft.  Substitution  in  For.  (21)  gives, 


~  (X'S  +  Xc}D' 


]  = 
0.05)0.077,3  -  (0.10  +  0.05)0.047,46] 


=  289.5[(0.925  X  0.077,3)  -  (0.15  X  0.047,46)]  =  289.5(0.071,5  - 

0.007,1) 
=  289.5  X  0.064,4  =  18.65  Ib.  per  i.h.p.  hr. 

131.  To  Find  The  Total  Steam  Used  By  An  Engine  Per 
Hour  multiply  the  weight  used  per  indicated  horse  power 
per  hour  for  head  and  crank  end  each  by  the  indicated  horse 
power  developed  by  the  steam  in  that  end  and  add  together 
these  two  products. 

EXAMPLE.  —  An  engine  shows,  at  the  head  end,  40.5  i.h.p.  and  20.2  Ib. 
per  i.h.p.  hr.  ;  at  the  crank  end,  38.8  i.h.p.  and  20.6  Ib.  per  i.h.p.  hr.  What 
is  its  total  steam  rate?  SOLUTION.  —  The  head  end  uses  40.5  X  20.2  = 
818  Ib.  per  hr.  The  crank  end  uses  38.8  X  20.6  =  799  Ib.  per  hr.  The 
engine,  therefore,  uses  818  +  799  =  1617  Ib.  per  hr. 

132.  More    Specific    Uses    Of    Indicators    And    Indicator 
Diagrams  As  Applied  To  Compound  Engines  will  be  treated 
in  Div.  8. 

QUESTIONS  ON  DIVISION  3 

1.  What  is  a  steam-engine  indicator? 

2.  What  uses  can  be  made  of  the  indicator  diagram? 

3.  What  determines  whether  a  pencil  mechanism  is  satisfactory  or  not? 

4.  When  should  an  outside  spring  indicator  be  used? 

G 


82       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div    3 

5.  Why  must  a  reducing  motion  be  used  in  connection  with  an  indicator? 

6.  What  is  a  brumbo  pulley  and  where  is  it  used? 

7.  What  is  a  pantograph? 

8.  What  must  be  the  direction  of  the  drum  cord  leading  from  a  pantograph? 

9.  What  is  the  principle  of  the  reducing  wheel? 

10.  What  precautions  must  be  taken  to  avoid  distortions  of  the  diagram  when  using 
reducing  wheels? 

11.  What  are  the  limitations  of  the  inclined-plane  reducing  mechanism? 

12.  What  two  tests  will  show  up  a  faulty  indicator  reducing  mechanism? 

13.  How  should  a  cylinder  be  piped  for  indicators? 

14.  Why  must  indicator  cocks  have  a  relief  passage? 

15.  Why  is  it  better  to  use  two  indicators  on  a  cylinder  than  only  one? 

16.  What  is  meant  by  the  "number"  of  an  indicator  spring? 

17.  Why  must  indicator  springs  be  tested? 

18.  How  can  indicator  springs  be  tested? 

19.  What  results  from  using  too  light  an  indicator  spring? 

20.  What  results  from  using  too  heavy  an  indicator  spring? 

21.  What  are  the  steps  in  assembling  an  indicator? 

22.  What  kind  of  paper  should  be  used  on  indicators? 

23.  What  sort  of  pencil  should  be  used  in  an  indicator? 

24.  What  does  an  atmospheric  line  show? 

25.  What  are  the  steps  in  taking  an  indicator  diagram? 

26.  What  "lines"  comprise  an  indicator  diagram 

27.  What  influences  the  appearance  of  the  admission  line? 

28.  What  causes  variations  in  the  steam  line? 

29.  What  is  a  steam-chest  diagram  and  what  does  it  show? 

30.  What  may  the  expansion  line  reveal? 

31.  What  form  should  the  expansion  line  have  if  an  engine  is  in  good  order? 

32.  What  do  the  release  and  exhaust  lines  indicate? 

33.  What  defects  in  an  engine  may  the  compression  line  reveal? 

34.  On  what  does  the  compression  pressure  depend? 

35.  How  can  the  mean  effective  pressure  be  found  without  a  planimetcr? 

36.  How  is  the  mean  effective  pressure  found  with  a  planimeter? 

37.  What  are  averaging  planimeters? 

38.  What  are  the  horse  power  constants  of  an  engine? 

39.  What  are  indicated,  brake,  and  friction  horse  power? 

40.  What  is  the  basis  of  determining  steam  consumption  from  indicator  cards? 

41.  Why  cannot  the  weight  of  steam  used  by  an  engine  be  accurately  determined 
from  indicator  cards? 

PROBLEMS  ON  DIVISION  3 

1.  With  the  pendulum  lever  mechanism  shown  in  Fig.  114,  what  length  diagram  will 
result?  What  must  be  the  radius  of  a  brumbo  pulley  on 
this  lever  to  give  a  diagram  3-in.  long? 

2.  What  length  of  indicator  diagram  will  be  produced 
by  the  reducing-wheel  mechanism  shown  in  Fig.  115? 

3.  By  the  method  of  ordinates  find  the  mean  height  of 
the  diagrams  shown  in  Fig.  1 16. 

4.  If  the   diagrams  of  Fig.  116  were  taken  with  a  60-lb. 
spring  what  are  the  mean  effective  pressures  shown? 

Fio.     114  (1)    What         '•  ^ne  diagrams  of  Fig.  116  are  from  an  engine  having  a 

length  will  the  diagram  str°ke  of  15  in.;  a  cylinder  12  in  in  diam.;  and  a  piston 
be?  (2)  What  radius  for  roc*  2^  in>  in  diam-  If  &  runs  at  22°  r.p.m.,  what  is  its 
brumbo  pulley?  horse  Power? 

6.  If  the   clearance  at  each  end  of  the  engine  of  Prob.  5 

is  15  per  cent,  of  the  piston  displacement,  construct  the  theoretical  expansion  curves 
beginning  at  points  C  and  D.  From  points  X  and  Y,  construct  the  theoretical  com- 
pression curves. 


SEC.  132] 


STEAM-ENGINE  INDICATORS 


83 


7.  From  the  results  of  Prob.  6  can  you  make  any  statement  as  to  the  conditions  of  the 
engine,  valves,  etc. 

8.  Find  the  steam  rates  for  the  crank  and  head  ends  of  above  engine  using  points  R,  S, 
X,  and  Y. 


:•  I 

k -—36" 'stroke - >| 


Vff//////////////////^ 

FIG.  115. — What  will  be  the  length  of  the  indicator  diagram? 


Atmospheric  Line--'' 
FIG.  116. — Find  the  mean  height  of  each  diagram. 

9.  Find  the  total  steam  used  per  hour  by  above  engine. 

10.  Trace  off  the  diagrams  of  Fig.  116  and  measure  the  areas  with  a  planimeter,  and 
find  the  mean  effective  pressures.     Compare  the  results  with  those  of  Probs.  3  and  4. 


DIVISION  4 
SLIDE  VALVES  AND  THEIR  SETTING 

133.  Slide  Valves  Are  Employed  In  Steam  Engines  Where 
Simplicity  And  Low  Price  Are  More  Important  than  the  actual 
economy  of  the  engine  in  its  use  of  steam.  Slide-valve 
engines  employ  but  one  valve  per  cylinder  and  a  compara- 
tively simple  valve-operating  mechanism,  whereas  engines  of 
greater  refinement  generally  employ  a  riumber  of  valves  per 
cylinder  (see  Div.  5)  and  require  a  more  complex  mechanism 
for  operating  the  valves.  The  scope  of  this  division  is  to 
discuss : 

(1)  How  slide  valves  function.  (2)  Terms  appertaining  to 
slide  valves  and  their  operating  mechanisms.  (3)  The  advan- 
tages and  disadvantages  of  slide  valves  of  various  types.  (4) 
Methods  of  adjusting  slide-valve  operating  mechanisms.  These 
adjustments  are  commonly  known  as  il valve  setting" 

134.  "Valve  Diagrams,"  (Bilgram,  Zeuner,  Reuleaux)  And 
"The  Valve  Ellipse"  are  names  given  to  graphical  methods  for 
proportioning  engine  valves  and  valve  mechanisms.     These 
diagrams   are   useful   chiefly  in  engine   designing,   which   is 
beyond  the  scope  of  this  book.     A  treatment  of  these  graphical 
methods  is  not  given  herein  because  they  are  of  little  value  to 
the  practical  operating  man.     For  a  discussion  of  valve  dia- 
grams see  VALVE  GEARS  by  C.  H.  Fessenden,  or  THE  DESIGN 
AND  CONSTRUCTION  OF  HEAT  ENGINES  by  W.   E.   Ninde. 

135.  The  Function  Of  The  Slide  Valve  Is,  as  explained  in 
Sec.  4,  to  open  and  close,  at  the  proper  instants,  passages 
through  which  steam  may  flow  into  or  out  of  the  engine 
cylinder.     This  slide  valve,  therefore,  permits  the  steam  to 
perform  its  cycle,  Sec.  102,  within  the  engine  cylinder.     Since  a 
slide  valve  performs  its  functions  in  the  same  manner  for  both 
ends  of  the  engine  cylinder,  the  following  explanation,  of  the 
method  whereby  a  slide  valve  controls  steam  flow  into  and  out 

84 


SEC.  135]        SLIDE  VALVES  AND  THEIR  SETTING 


85 


of  the  head  end  of  a  cylinder,  is  descriptive  of  its  performance 
for  both  ends. 

EXPLANATION. — In  Fig.  117,  the  valve,  V,  is  shown  moving  to  the  right 
and  is  ready  to  admit  high-pressure  steam  from  the  steam  chest,  S}  to 

, Exhaust  Port 

Valve   \    Steam    Slide      Direction  of 
-.  Chesty  Valve*    [Valve  Mot  ion 


Piston-' 


^Direction  of 
Piston  Motion 


FIG.  117. — Point  of    head-end  admission — steam  about  to  enter  the  head  end  of  the 

cylinder. 

the  head-end  cylinder  port,  H,  and  thence  to  the  head-end  of  the  cylinder. 
The  steam  will  then  force  the  piston,  P,  toward  the  right.  In  the  position 
shown  in  Fig.  118,  V  has  been  moved  to  the  right,  stopped,  and  is  now 
moving  to  the  left.  It  has  returned  to  its  former  position.  Up  to  this 
point,  high-pressure  steam  has  been  admitted  to  the  head-end  of  the 


High- 
Pressure 
Ste 


^Exhaust  Port 
•      .-Slide     .-Direction.  Of 


tValre  Motion 


"High -Pressure  Steam 
About  To  Expand 

FIG.  118. — Point  of  head-end  cut-off — steam  supply  from  the  steam  chest  has  just  been 
cut  off  from  the  head  end  of  the  cylinder. 

cylinder.  As  V  moves  farther  to  the  left,  no  more  steam  will  be  admitted 
to  H  because  V  completely  shuts  it  off  from  S.  Hence,  since  the  head- 
end of  the  cylinder  is  isolated  from  the  high-pressure  steam,  the  piston 
continues  to  move  toward  the  right  due  only  to  pressure  of  the  expanding 
steam  in  the  head-end  of  the  cylinder. 


86       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


When,  as  shown  in  Fig.  119,  the  piston  has  almost  reached  the  end  of  its 
stroke,  traveling  toward  the  right,  any  further  movement  of  the  valve 
toward  the  left  will  allow  the  expanded  steam  in  the  head-end  of  the 
cylinder  to  flow  through  H  to  the  exhaust  port,  E.  High-pressure  steam 
is  about  to  be  admitted  to  the  crank-end  of  the  cylinder  where  it  will  force 

^-Exhaust  Port 

.-Slid?      .-Direction  Of 
:  Valve  Motion 


*       Direction  Of 

Piston  Motion  " 


^Expanded  Steam 

Fia.   119. — Point  of  head-end  release — expanded  steam  in  the  head  end  of  the  cylinder 
about  to  be  released  or  exhausted  into  the  exhaust  port. 

the  piston  toward  the  left.  Fig.  120  shows  the  position  of  the  piston  and 
valve  after  the  expanding  steam  in  the  crank-end  of  the  cylinder  has 
forced  the  piston  to  the  left.  The  valve  has  been  moved  to  the  left, 
stopped,  and  is  now  moving  to  the  right  again.  Further  movement  of 
the  valve  toward  the  right  will  shut  off  the  head-end  of  the  cylinder  from 


High- 
Pressure   Si-earn 


Steam*     Chest-, 


,  -Exhaust  Port 

5lide          Direction   Of 
Valve-         'Valve  Motion 
98B 


^'Expanded  Steam  ^Expanding 

About  To  Be    Compressed         Steam 

FIG.   120. — Point  of  head-end  compression — the  expanded  steam  remaining  in  the  head 
end  of  the  cylinder  is  about  to  be  compressed  by  the  piston. 

E,  thus  confining  the  remaining  steam  in  the  head-end  of  the  cylinder  to 
serve  as  a  '  compression"  cushion  for  the  piston  as  it  approaches  the  end 
of  its  travel. 

NOTE. — THE  POINTS  OF  " ADMISSION,"  "CUT-OFF,"  "RELEASE,"  AND 
"COMPRESSION"  are  understood  to  be  the  positions  of  the  engine  mechan- 


SEC.  136]        SLIDE  VALVES  AND  THEIR  SETTING 


87 


ism  and  the  corresponding  positions  of  the  indicator  pencil  on  the 
indicator  diagram  (Fig.  88)  when  the  valve  is  in  the  act  of  opening  or 
closing  the  cylinder  port.  The  positions  of  the  slide  valve  at  each  of  these 
points  are  shown  in  Figs.  117  to  120.  Obviously  there  will  be  one  of  each 
of  these  points  for  each  end  of  the  cylinder.  These  are  specified  as  head- 
end admission,  crank-end  admission,  head-end  cut-off,  etc. 

136.  The  Terms  "Outside -Admission"  Or  "Direct"  And 
"Inside -Admission"    Or    "Indirect"    As    Applied    To    Slide 

Valves  relate  to  the  manner  in  which  steam  is  admitted  to  the 
cylinder.  Thus  an  " outside-admission "  or  " direct"  valve 
(Fig.  121)  is  one  which  has  live,  or  boiler-pressure  steam,  S, 
beyond  the  two  ends  of  the  valve  and  exhaust  steam  between 


Outside  Edge 
•Of  Valve 


Exhaust       Live  Steam       /lnside  Edge 
Steam*         -Space -^  ,'    Of  Valve 


Exhaust'  \        ^  Inside 

\      Port  ;    Edge  Of  Valve 

*Cy finder  Ports  •' 

Fia.   121. — An   outside-admission   slide 
valve. 


Valve 
FIG.   122. — An  inside-admission  slide  valve. 


the  two  ends  of  the  valve.  Steam  enters  the  cylinder  past 
the  outside  edges,  0,  of  the  valve  and  exhausts  from  the 
cylinder  past  the  inside  edges,  I.  An  "  inside-admission " 
or  "indirect"  valve  (Fig.  122)  is  one  which  has  exhaust 
steam,  E,  at  the  two  ends  of  the  valve  and  live  steam  between 
the  two  ends  of  the  valve.  Steam  enters  the  cylinder  past 
the  inner  edges,  7,  of  the  valve  and  exhausts  from  the  cylinder 
past  the  outside  edges,  0. 

NOTE. — "EXTERNAL,"  AND  "INTERNAL"  ARE  OTHER  TERMS  APPLIED 
To  SLIDE  VALVES  to  denote  whether  they  are  of  the  inside  or  outside 
admission  type.  Outside-admission  valves  are  sometimes  called  external. 
Also  inside-admission  valves  are  sometimes  called  internal  Piston  slide 
valves  are  practically  always  designed  for  inside  admission  (indirect) 
whereas  other  slide  valves  are  nearly  always  of  the  outside-admission 
(direct)  type. 

137.  The  Advantages  And  Disadvantages  Of  Plain  D -Slide 

Valves  may  be  briefly  stated  thus:  (1)  Advantages,     (a)  Con- 


88       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

struction  is  very  simple.  (6)  Operating  mechanism  is  simple, 
(c)  Maintenance  is  low,  because  of  the  simplicity.  (2)  Dis- 
advantages, (a)  Because  of  unequal  pressures  on  the  two 
sides,  D-slide  valves  are  forced  strongly  against  their  seats; 
this  is  likely  to  produce  excessive  friction  and  wear  at  the  seat. 
(6)  Cylinder  ports  are  opened  and  closed  slowly;  this  is  the 
cause  of  wire-drawing  or  throttling  of  the  steam,  especially 
at  cut-off,  (c)  Admission,  cut-off,  release  and  compression 
are  not  independently  adjustable.  That  is,  adjustment  say 
of  head-end  cut-off  is  likely  to  affect  the  adjustment  of  all 
events  of  both  ends  of  the  cylinder,  (d)  Engines  with  D-slide 
valves  must  have  comparatively  large  clearance  volumes. 
(e)  Because  of  unequal  temperatures  on  the  two  sides  of  the 
valves,  D-slide  valves  are  apt  to  warp.  This  makes  them 
unsuited  to  engines  which  operate  on  superheated  steam. 

NOTE. — THE  DISADVANTAGES  OF  D-SLIDE  VALVES  MAY  BE  PARTIALLY 
OVERCOME  by  using  slide  valves  of  certain  special  types  which  are  dis- 
cussed in  the  following  sections.  But  no  one  of  these  special  types 
eliminates  entirely  all  of  the  disadvantages.  The  valve  designs  dis- 
cussed in  Div.  5  afford  the  most  logical  means  for  overcoming  the 
disadvantages  listed  above. 

138.  Advantages  And  Disadvantages  Of  Piston  Slide  Valves  : 

(1)  Advantages,  (a)  Construction  is  almost  as  simple  as  that 
of  the  D-slide  valve.  (6)  Operating  mechanism  is  simple, 
(c)  Steam  pressure  does  not  produce  any  unbalanced  force  on 
the  valve,  (d)  Temperatures  on  different  parts  will  not 
distort  the  valve;  it  is  therefore  suited  for  superheated  steam. 
(e)  Maintenance  is  low,  because  of  the  simplicity.  (2)  Dis- 
advantages, (d)  Cylinder  ports  are  opened  and  closed  slowly. 
(6)  Valve  events  are  not  independently  adjustable,  (c) 
Clearance  volume  of  engine  must  be  very  large,  (d)  Wear  of 
the  valve  or  its  seat  is  apt  to  cause  leakage  past  the  valve  and  is 
difficult  to  take  up;  frequently  wear  necessitates  replacement 
of  the  valve  or  its  seat. 

NOTE. — PISTON  VALVES  ARE  USUALLY  OF  THE  INSIDE-ADMISSION 
TYPE.  With  inside  admission  (Fig.  33)  the  stuffing  box  on  the  valve 
stem  seals  the  opening  only  against  exhaust  steam,  whereas  with  outside 
admission  (Fig.  21)  the  stuffing  box  holds  high-pressure  steam.  Leaks  at 
the  stuffing  boxes  of  inside-admission  valves  do  not,  therefore,  waste  steam 
because  the  leaking  steam  has  already  been  used  by  the  engine.  D-slide 


SEC.  139]        SLIDE  VALVES  AND  THEIR  SETTING 


89 


valves  cannot  be  of  the  inside-admission  type  because  high-pressure 
steam,  if  within  the  D,  would  raise  the  valve  off  its  seat  and  would  thus 
escape,  without  doing  work,  into  the  exhaust  passage. 

139.  Advantages  And  Disadvantages  Of  Balanced  Slide 
Valves  (Fig.  123) :  (1)  Advantages,  (a)  Construction  is  almost 
as  simple  as  that  of  the  plain  D-slide  valve.  (6)  Operating 
mechanism  is  simple,  (c)  Pressure  of  the  steam  on  the  two 
sides  of  the  valve  is  nearly  balanced ;  therefore,  friction  and 
wear  are  less  than  with  D-slide  valves,  (d)  Valve  is  not  so 
badly  distorted  by  temperature  differences  on  its  surfaces 


*• Cylinder  Ports---'' 
FIG.  123. — A  balanced  slide  valve. 

as  is  a  plain  D-slide  valve,  (e)  Maintenance  is  low  and  com- 
pensation for  wear  is  automatic.  (2)  Disadvantages,  (a) 
Cylinder  ports  are  opened  and  closed  slowly.  (6)  Valve 
events  are  not  independently  adjustable,  (c)  Clearance 
volume  must  be  large,  though  not  larger  than  with  the  plain 
D-slide  valve,  (d)  Steam  leakage  at  the  valve  is  likely  to  be 
greater  than  with  plain  D-slide  valves. 

EXPLANATION. — Since  the  exhaust  steam  enters  S  (Fig.  123)  through 
balance  hole,  0,  the  downward  pressure  on  V,  due  to  the  exhaust  steam 
within  the  area  enclosed  by  ring,  R,  is  practically  the  same  as  the  upward 
pressure  on  V  due  to  the  exhaust  steam  in  the  exhaust  cavity,  C.  Hence 
the  pressure,  due  to  the  exhaust  steam,  which  V  exerts  against  X  u 
practically  zero. 

Now,  P  is  held  rigidly  in  position  by  bolts,  B.  Therefore,  the  live 
steam  in  steam  space  L  can  exert  no  downward  pressure  within  the  area 


90       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

enclosed  by  R.  The  only  downward  pressure  which  the  live  steam  can 
exert  is  that  exerted  downward  on  that  projected  area  of  V  which  is 
outside  of  R.  This  area  outside  of  R  is,  in  actual  engines,  relatively 
small;  in  fact  it  can  be  made  practically  zero  if  the  ring,  R,  is  arranged 
around  the  extreme  edge  of  V. 

But  in  actual  engines  it  is  desirable  that  there  be  some  downward 
thrust  of  V  against  X  to  hold  V  snugly  against  its  seat  to  prevent  leakage. 
In  actual  engines,  the  projected  area  of  V  which  is  outside  of  R  is  so  made 
by  the  engine  designer  that  the  resultant  downward  pressure  of  V  and  X 
is  sufficient  to  effectively  prevent  this  leakage  but  still  not  induce  exces- 
sive friction  between  V  and  X.  If  some  live  steam  leaks  from  L  past  R 
into  S,  it  passes  through  0  to  the  exhaust.  Thus  0  prevents  the  pressure 
in  S  becoming  greater  than  the  exhaust  pressure. 


Pressure  Plate-          Spring^         .-Live-Steam  Space 


Ba/arnced 
Doub/e  -Ported 
Valve- 


FIG.  124. — Longitudinal  section  of  Sweet  valve  (Erie  Ball  Engine  Co), 
same  valve  as  is  shown  in  Fig.  125. 

140.  Advantages  And  Disadvantages  Of  Multiported  Slide 
Valves  (Fig.  32,  see  Sec.  44  for  definition)  are:  (1)  Advantages, 
(a)  Construction  is  almost  as  simple  as  that  of  plain 
D-slide  valve.  (6)  Operating  mechanism  is  simple,  (c) 
Cylinder  ports  are  opened  and  closed  more  quickly  than  with 
the  valves  already  discussed,  (d)  Valve  travel  need  not  be  so 
great  as  with  single-ported  valves;  this  means  that  less  power 
will  be  required  to  slide  the  valve  on  its  seat.  (2)  Disadvan- 


SEC.  141]       SLIDE  VALVES  AND  THEIR  SETTING 


91 


tages.  (a)  Unless  the  valve  is  balanced,  see  note  following, 
the  steam  pressure  is  likely  to  cause  excessive  friction  and  wear 
at  the  seat  and  also  to  cause  distortion  of  the  valve,  (b) 
Valve'  events  are  not  independently  adjustable,  (c)  Clear- 
ance volume  must  be  large. 


Engine 
Cylinder 


Va/ve      5weet 
Seat,     'Valve 


.-Pressure  Plate 
"\  (Balance  P/ate) 


I-Sectional 
Elevation 


FIG.   125. — Transverse  section  and  side  view  of 
Sweet  valve. 


NOTE.— BALANCED  MULTI- 
PORTED  VALVES  COMBINE  THE 
FEATURES  OF  THE  BALANCED 
AND  THE  MULTIPORTED  slide 
valves.  Figs.  124  and  125  show 
a  modern  form  of  balanced  mul- 
tiported  valve.  It  is  to  be  noted 
that  in  this  valve  the  auxiliary 
ports  affect  only  the  admission 
of  high-pressure  steam  to  the 
cylinder.  The  exhaust  steam 
passes  through  only  a  single 
valve-port.  Some  balanced  multiported  valves  also  exhaust  through 
an  auxiliary  port. 

141.  Advantages   And  Disadvantages   Of  Riding-Cut-Off 
Slide  Valves  (Fig.  34) :  (1)  Advantages,     (a)  Cut-off  is  effected 
rapidly;  that  is,  cut-off  takes  place  when  the  riding  blocks  are 
near  their  mid-travel  position  and  travelling  relatively  fast. 
(b)  Cut-off  can  be  effected  at  the  same  fraction  of  both  the 
forward  and  the  return  stroke ;  thus,  the  work  done  in  the  two 
ends  of  the  cylinder  can  be  equalized,     (c)  The  construction 
of  the  cylinder,  valves,  and  their  operating  mechanism  is 
simpler  than  with  other  engines  which  have  advantages  (a) 
and  (6) .     (2)  Disadvantages,     (a)  Except  when  made  in  piston 
form — as  in  the  Buckeye  engine — the  valve  is  unbalanced 
and  presents  two  surfaces  along  which  excessive  friction  may 
act;  hence  much  power  is  required  to  move  the  valves  and 
wear  may  be  excessive,     (b)  Engine  clearance  is  large,     (c)  The 
valve-operating  mechanism  consists  of  twice  as  many  parts  as 
does  that  for  a  simple  slide  valve;  hence,  the  riding-cut-off 
valve  is  apt  to  give  more  trouble  and  require  more  attention. 

142.  Features  Of  The  Gridiron -Valve  Engine  (Figs.  126  to 
128)  arc  that:  (1)  The  valves  require  small  movement  (from  J^  in. 
to   \}^   in.).     (2)   Having  four  valves  and  two  eccentrics ,   all 
events  of  both  ends  of  the  cylinder  are  independently  adjustable. 


92       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


SEC.  142]        SLIDE  VALVES  AND  THEIR  SETTING 


93 


(3)  Clearance  is  very  small  (usually  less  than  with  Corliss 
valves).  (4)  The  valve-operating  mechanism  permits  of  high 
engine  speeds.  (5)  Cut-off  occurs  quickly,  while  the  valves  are 
moving  fast,  and  it  is  the  only  event  that  need  be  changed 
during  governing.  Its  chief  disadvantages  are  that  the  valve- 
operating  mechanism  is  relatively  complex,  the  construction 
of  the  engine  makes  it  costly,  and  adjustment  of  the  valve- 
mechanism  is  relatively  difficult. 

EXPLANATION. — In  the  Mclntosh  Seymour  Engine  (Figs.  126  to  128) 
each  cylinder  has  four  main  valves — two  steam  and  two  exhaust — and 


'Link  'Shaft 
''Shaft 

FIG.   127. — Section    through    head    of    Mclntosh    &  Seymour  engine  showing   main- 
valve  operating-mechanism. 

two  auxiliary  or  riding-cut-off  valves,  all  of  which  are  of  gridiron  construc- 
tion. The  four  main  valves  are  driven  from  a  main  rock  shaft,  M ,  (Fig. 
127)  which  is  rocked  by  the  mechanism  of  Fig.  126  from  a  fixed  eccentric, 
F,  on  the  crank  shaft.  The  main  valves  control  the  points  of  admission, 
release,  and  compression  which  can  be  adjusted  independently  for  each 
end  of  the  cylinder.  The  auxiliary  or  riding  cut-off  valves  are  driven 
from  another  rock  shaft,  A,  (Fig.  128)  which  is  operated  from  a  governor- 
controlled  eccentric,  G,  as  shown  in  Fig.  126.  The  motions  derived  from 
the  eccentrics  are  so  distorted  by  the  several  links  that  the  valves  move 
quickly  in  opening,  pause  when  full  open,  and  remain  almost  stationary 
when  closed. 


94       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

NOTE. — THE  SETTING  OF  GRIDIRON  VALVES  is  rather  complex  and 
will  not  be  discussed  in  this  book  for  lack  of  space.  The  reader  is,  there- 
fore, referred  to  the  manufacturer  for  instructions  for  setting  gridiron 
valves. 


Shaft'' 


FIG.   128. — Section  through  head  of  Mclntosh  &  Seymour  engine  showing  cut-off-valve 
operating-mechanism. 


Valve  in  Mlda 'le 
of  its   Travel^ 


Head-End..1          '''Exhaust         'Crank-End 
Cylinder  Port       Space          Cylinder  Port 

FIG.    129.  —  Outside-admission    (D-slide) 
valve  showing  lap. 


Head-  End  Steam 
f  Lap. 

Head-    A        -' 
End      ^ir     /I 

Exhaust, \  |  jH5 
^-j"  |  I  1 


Crank- End  Steam 
Lap^ 


. \\Exhaust 
I  I    Laf> 


"Exhaust      \    "'Valve       ''-Live       "Crank- 
Space  '-  in  Middle    Steam    End 
Head- End       \"f '*        5Pace     C^er 
CylinderPorf  Trave'  Hort       . 
Exhaust  Space ' 


FIG.  130. — Inside-admission  (piston)  valve 
showing  lap. 


143.  Valve  "Lap"  is  (Figs.  129  and  130)  the  amount  (length) 
by  which  a  valve  overlaps  or  extends  beyond  the  cylinder 
port  when  the  valve  is  mid-way  between  its  extreme 


SEC.  144]        SLIDE  VALVES  AND  THEIR  SETTING 


95 


positions.  As  a  slide  valve  has  four  edges  with  which  it  cuts 
off  steam  flow,  there  will  be  valve  lap  measured  to  each  of 
these  edges.  Various  terms  which  are  used  to  designate  the 
lap  at  the  different  points  are  defined  graphically  in  the  follow- 
ing illustrations:  exhaust  lap  and  steam  lap,  Figs.  129  and  130; 
inside  lap  and  outside  lap,  Figs.  131  and  132. 

0-  >j  \f  -  -  Outside  Lap    -  >|  \<-  Q 

Exhaust  I  \ --^-Inside  Lap  A\\<-\  \ -Exhaust 
\Space\\     l|  I  I     I  \\sf*ice 


0->|  Y-  -Out  side  Lap  ---- 


Valve  in 
Hiddeof\  | 

Trt 


Head -End     \     Exhaust         Crank -End 
Cylinder  Port'     Space       Cylinder  Port 

FIG.  131. — Illustrating  inside  and  out- 
side lap  of  an  outside-admission  CD- 
slide)  valve. 


Valve  in         ^Head-End  V/W      'Crank- End 
Middle  of       Cylinder     steam     cylincler 
its  Travel        &rt  |J£J     Port 

FIG.  132. — Illustrating  inside  and  out 
side  lap  of  an  inside-admission  (piston) 
slide  valve. 


in  Middle 
°    fs7ve' 


NOTE. — INSIDE  CLEARANCE  OF  A  SLIDE  VALVE  (Fig.  133)  is  the 
amount  (length)  of  opening,  N,  of  the  cylinder  ports  to  the  exhaust  pas- 
sage, E,  when  the  valve,  V,  is  mid-way  between  its  extreme  positions.  It 
is  the  exact  opposite  of  inside  lap  and  is  sometimes  called  negative  lap. 
Inside  clearance  permits  of  very  early  release  and  late  compression. 

144.  The    Purposes    Of    Steam  And    Exhaust    Lap    Are: 

(1)  Steam  lap  enables  a  valve  to  cut  off  the  high-pressure  steam 
supply  to  the  cylinder  before  the  piston  reaches  the  end  of  the 
stroke.  In  other  words  it  per- 
mits the  use  of  steam  expan-  Head-End 
sively,  Sec.  15.  (2)  Exhaust 
lap  delays  release  and  brings 
about  earlier  compression  in 
engines  where  the  valves  have 
sufficient  steam  lap  to  effect  a 
desirable  cut-off.  Increased 
steam  lap  necessitates  greater 
valve  movement  which  in  turn  provides  a  longer  exhaust 
period.  In  engines  with  valves  which  have  plenty  of  steam  lap 
but  no  exhaust  lap,  the  working  steam  in  the  cylinder  would  be 
released  too  early,  thus  preventing  the  proper  steam  expansion. 


FIG.   133. — A  slide  valve  with  negative  ex- 
haust lap  or  "inside  clearance." 


96       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


145.  To  Change  The  Lap  Of  A  Slide  Valve  it  is  necessary  to 
either  cut  away  part  of  the  valve  or  add  to  the  valve.     As  it  is 
usually  very  expensive  to  add  to  the  valve,  a  new  valve  would 
usually   be    procured    whenever   this   is   necessary.     Engine 
valves  should  always  be  furnished  by  their  manufacturers 
with  the  proper  lap  to  suit  the  operating  conditions.     There- 
fore, it  is  seldom  necessary  to  change  the  lap  of  a  valve  except 
when  the  engine  is  to  be  used  under  steam  pressures  different 
from  those  for  which  it  was  designed.     If,  however,  it  does 
become  necessary  to  change  the  valve  dimensions,  the  best 
procedure  is  to  have  the  engine  builder  furnish  a  new  valve 
to  suit  the  new  conditions.     If  the  manufacturer  cannot  be 
reached  and  if  it  is  firmly  established  that  the  valve  lap  must 
be  changed,  then  the  changes  may  be  made  in  accordance  with 
Table  146. 

146.  Table  Showing  Effects  Of  Changing  Valve  Lap.— The 
lap  should  always  be  changed  by  equal  amounts  on  both  the 
head-end  and  the  crank-end  cutting  edges. 


Lap  change 

Effect  on  point  of 

Admission 

Cut-off 

Release 

Com- 
pression 

Steam  lap  

Increased 
Decreased 

Later 
Earlier 

Earlier 
Later 

Unchanged 
Unchanged 

Unchanged 
Unchanged 

Exhaust  lap  

Increased 
Decreased 

Unchanged 
Unchanged 

Unchanged 
Unchanged 

Later 
Earlier 

Earlier 
Later 

147.  "Lead"  Is  Understood  To  Mean  the  amount  (length, 
Fig.  134)  by  which  a  valve,  V,  opens  a  cylinder  port  for  the 
admission  of  supply  steam  when  the  piston  is  exactly  at  the  end 
of  its  stroke  within  the  engine  cylinder.  Unlike  lap,  lead  is 
not  determined  by  the  dimensions  of  the  valve.  Lead  is 
determined  wholly  by  the  adjustment  of  the  valve  mechanism. 
The  purpose  of  so  adjusting  the  valve  that  it  provides  lead 
is  to  insure  that  steam  will  enter  the  cylinder  shortly  before  the 
piston  reaches  the  end  of  a  stroke.  The  objects  of  thus  admit- 
ting the  steam  are:  (1)  To  have  it  aid,  by  its  compression,  in 
bringing  the  piston  to  rest  before  its  reversal  in  direction  of 


SEC.  148]        SLIDE  VALVES  AND  THEIR  SETTING 


97 


motion.     (2)   To  insure  full  steam-supply  pressure  behind  the 
piston  as  it  begins  its  next  stroke. 

EXPLANATION. — It  requires  a  short  time  interval  for  sufficient  steam  to 
enter  the  cylinder  to  completely  fill  the  clearance  volume  to  supply 
pressure.  If  steam  were  first  admitted  to  the  port,  just  as  the  piston 
reached  the  end  of  its  stroke,  the  momentum  of  the  flywheel  would  cause 


Valve       .-Lead 


Piston  At 
End  Of  Stroke' 

FIG.  134. — Engine  on  head-end  dead  center  showing  head-end  lead. 

the  piston  to  recede  from  the  cylinder  end  before  enough  steam  were 
admitted  to  fill  the  clearance  volume.  If,  however,  the  cylinder  port  is 
opened  shortly  before  the  piston  reaches  the  end  of  the  stroke,  the 
pressure  within  the  clearance  volume  will  rise  to  supply  pressure  before 
the  piston  leaves  the  end.  Thus  lead,  or  earlier  opening,  adds  to  the 
pressure  behind  the  piston  during  the  first  part  of  the  stroke,  and  there- 
fore adds  to  the  work  done  by  the  steam  on  the  piston  (Div.  1). 

148.  The  Slide  Valve  Usually  Receives  Its  Motion  From  An 
Eccentric  (E,  Fig.  135)  which  is  attached  to  the  engine  shaft, 


Va/i/e         Slide 
:Seat        :' Valve 


\:-,.Yalve5tem          MyValve  Block ' 

j/"  ^Eccentric  Rodr* 

,-G  Crankshaft-/ 

•'-Valve- Block  ''$ 

Guide  Eccentric-'' 

FIG.  135. — Eccentric  mechanism. 


S.  The  valve,  V,  and  valve  block,  B,  are  fastened  to  opposite 
ends  of  the  valve  stem,  I.  B  serves  the  same  purpose  as  does 
the  crosshead  in  the  standard  engine  crank-mechanism.  The 
eccentric  rod,  R,  is  fastened  at  one  end  to  B  and  at  the  other 
end  to  the  eccentric,  E.  Thus  the  motion  of  the  eccentric  is 
transmitted  through  R,  B,  and  I  to  the  valve  V. 


98       STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


NOTE.  —  THE  ECCENTRICITY  OR  THROW  OF  AN  ECCENTRIC  (Fig.  136)  is 
the  distance,  R,  between  the  center  of  the  crank  shaft  and  the  center  of  the 
eccentric  itself.  It  can  be  considered  as  the  distance  the  eccentric  is 
"off-center"  from  the  crank  shaft.  The  circle  of  radius  R  (Fig.  136)  is 
called  the  eccentric  circle. 

149.  The  Motion  Derived  From  An  Eccentric  is  equivalent 
to  that  from  a  crank  whose  radius  is  equal  to  the  throw  of  the 
eccentric.  That  this  is  true  is  demonstrated  below. 


Direction  Of  Rotation^      .Eccentric  Circle 
Eccentric  Rod* 


Crank 

<r/v         Valve     Direction  of  Circle 

5l'de       Stern  Rotation--^    .  Kx/ius 


Valve, 


Position  I  ^S&Cccentric 

(Very     :<+    \ 
Nearly)'  K«J 

Center  Of  Eccentric-./^ '^^ 
Eccentric  J-^\ 

=£sfe4t1> 

_a^C-x^     -~CeZterOf^     ^' 
'W/jk'^/////////      Crank  Shaft 

HC    . 

Position  n 

Center  Of    \'+'\ 
Eccentric-.. 

Center  Of 


'•^%-f^  Connecting  Rod-, 
'////fo^ValveSeat 


Position  I 

crfVery  Nt 


'(2R)*1       Position  M 

FIG.   136. — Illustrating  valve  travel  with 
eccentric  motion. 


h*1 

Crank  Circle-^''^^ 

>•(£» 


Y-- -.*>-){  Radius**' 

(2R)        Position  m 

FIG.   137. — Showing  valve  operated  by  a 
crank  on  the  shaft. 


EXPLANATION. — In  Fig.  136,  an  eccentric  attached  to  a  slide  valve  is 
shown  in  three  successive  positions.  The  eccentricity  is  represented 
by  the  distance,  R.  As  the  eccentric  moves  from  Position  /  to  Position 
//,  the  valve  moves  the  distance  a.  Likewise,  as  the  eccentric  moves 
from  position  7  to  Position  ///,  the  valve  moves  the  distance  6.  In  Fig. 
137  the  same  valve  is  shown  attached  by  a  connecting  rod  to  a  crank. 
This  crank  has  a  crank-arm  length,  BC,  or  distance  from  the  center  of 
the  crank  pin  to  the  center  of  the  crank  shaft  which  is  represented  by  R. 
The  distance,  R,  in  Fig.  137  is  the  same  as  the  throw,  R,  of  the  eccentric 
in  Fig.  136.  As  the  crank  in  Fig.  137  moves  from  Position  7  to  Position 
77,  the  valve  moves  the  distance  a.  As  the  crank  moves  from  Position  7 
to  Position  777,  the  valve  moves  the  distance  b.  Measurement  will  show 
that  the  distances  a  and  6  in  Fig.  136  are  the  same  as  the  distances  a  and 
6  in  Fig.  137.  Hence,  an  eccentric  motion  is  equivalent  to  a  crank  motion 
and  an  eccentric  can  be  considered  as  a  developed  form  of  the  crank  with 
the  crank  pin  sufficiently  enlarged  to  encircle  the  crank  shaft. 

150.  Valve  "Travel"  Can  Be  Denned  (Fig.  136)  as  the  dis- 
tance between  its  extreme  positions  or  the  distance  the  valve 


SEC.  151]        SLIDE  VALVES  AND  THEIR  SETTING  99 

moves  in  one-half  revolution  of  the  eccentric.  Thus  in  Fig. 
136,  7,  the  slide  valve  is  shown  in  a  position  with  the  eccentric, 
E,  in  its  head-end  extreme  position.  In  III,  E  is  in  its  crank- 
end  extreme  position.  The  distance  2R  through  which  the 
slide  valve  has  moved  during  the  shifting  of  the  eccentric  from 
I  to  III  is  its  travel. 

NOTE. — THE  TRAVEL  OF  A  VALVE  Is  EQUAL  To  TWICE  THE  "ECCEN- 
TRICITY" OR  "THROW"  OF  ITS  ECCENTRIC.  R,  Fig.  136,  is  the  eccen- 
tricity or  throw  of  the  eccentric  and  is  the  radius  of  the  circle 
described  by  the  eccentric  center.  In  some  engines,  intermediate  levers 
or  rocker  arms  are  introduced  between  the  eccentric  and  the  slide  valve; 
see  Fig.  291.  In  such  construction,  the  valve  travel  is  not  necessarily 
equal  to  twice  the  eccentricity. 

151.  The  Angle  Of  Advance  (Figs.  140  and  141)  is  the  angle 
through  which  the  eccentric  must,  when  the  piston  is  at  one  end 
of  its  stroke,  be  rotated  on  its  crank  shaft  to  draw  the  valve  from  the 


Eccentric 


Direction  of  Rotation-'*  ~  7  ' 


FIG.  138.  —  Valve  in  mid-travel  position  with  crank  on  head-end  dead  center.     (Advance 

angle  =  0.) 

middle  of  its  travel  to  its  operating  position.  In  other  words, 
the  angle  of  advance  is,  when  the  engine  is  at  one  end  of  its 
stroke  (on  dead  center)  the  angle  between  an  imaginary  line 
which  is  drawn  through  the  eccentric  and  the  crank-shaft 
centers  and  another  imaginary  line  which  is  drawn  through  the 
crank-shaft  center  and  at  right  angles  to  the  cylinder  axis. 

EXPLANATION.  —  In  Fig.  138  an  engine  is  shown  with  its  eccentric  so 
set  that  its  advance  angle  is  zero.  The  piston  is  at  its  extreme  head-end 
position.  The  slide  valve,  V,  is  in  the  middle  of  its  travel  and  the 
eccentric  center  line,  AB,  is  perpendicular  to  the  cylinder  axis  line  OL. 
It  is  evident  that,  with  the  valve  in  the  position  shown,  the  engine  will 
not  operate  properly  since  no  steam  is  being  admitted  to  the  cylinder 


100     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

when  the  piston  is  at  the  end  of  its  stroke.  To  insure  proper  operation, 
the  eccentric  must,  as  will  be  shown,  be  shifted  forward  through  a 
sufficient  angle  to  allow  steam  to  enter  the  cylinder. 

In  Fig.  139  the  crank,  C,  is  shown  in  its  original  position  but  the 
eccentric  has  been  shifted  forward  through  a  sufficient  angle  to  move  V 
forward  a  distance  equal  to  its  steam  lap.  The  center  line  of  the  eccentric 
in  the  new  position  is  DF.  The  angle,  AMD,  through  which  it  was 


Valve  Moved  Forward  a 
Distance  Equal  to  its  Lap 


Eccen  trie  Center  L  ine  - . 
Lap  Angle '''  j^\    p/<  ' 
Eccentr 


FIG.   139. — Valve  moved  forward  a  distance  equal  to  its  lap  with  crank  on  head-end 
center.     The  lap  angle  is  shown  here.     (Lead  angle  =  0). 


necessary  to  shift  the  eccentric  to  move  the  valve,  V,  a  distance  equal  to 
its  lap  is  called  the  lap  angle.  But  this  setting  of  the  valve  provides  no 
lead,  (Sec.  147). 

Now  since,  to  insure  satisfactory  operation,  all  engines  must  have  a 
definite  amount  of  lead  (Sec.  147)  the  eccentric  must  again,  to  provide 
this  lead,  be  shifted  ahead  from  the  position  shown  in  Fig.  139  to  that 
shown  in  Fig.  140.  The  additional  angle,  DMH,  through  which  the 
eccentric  has  been  shifted  from  position,  DF  (Fig.  139)  to  obtain  the  lead 


V\-Va/ve  Moved  Forward  a  Eccentric  Center  Line, 

•  Distance  Equal  to  Lap  +  Lead  .  .  D  <'' 

Angle  of  Advance---  -  ^'.'/V  H 


Center-/'/ 

ef  B' 

FIG.   140. — Valve  moved  forward  a  distance  equal  to  the  sum  of  its  lap  and  lead  with 
crank  on  head-end  center.     Lap  angle,  lead  angle,  and  angle  of  advance  are  shown. 


is  called  the  Lead  Angle.  The  Angle  Of  Advance,  AMH,  as  defined  above 
is  therefore  the  angle  between  the  eccentric  positions  AB  and  GH  and  is 
equal  to  the  sum  of  the  lap  angle  and  the  lead  angle  as  shown  in  Fig.  140. 

NOTE. — WITH  INSIDE-ADMISSION  VALVES  THE  ANGLE  OF  ADVANCE 
(Fig.  141)  is  determined  by  the  same  rule  (above).  It  is  to  be  observed, 
however,  that  with  inside-admission  valves  the  eccentric  lags  behind  the 


SEC.  152]        SLIDE  VALVES  AND  THEIR  SETTim: 


101 


crank  by  the  angle  OMH  =  QQdeg. — angle  of  advance — whereas,  with 
outside-admission  valves  the  eccentric  leads  the  crank  by  the  angle  OMH 
(Fig.  140)  =  90  deg.  +  angle  of  advance. 

NOTE. — THE  "DISPLACEMENT"  OF  A  SLIDE  VALVE  is  the  distance  that 
the  valve  has,  at  any  instant,  been  moved  from  its  central  position. 
Thus,  when  an  engine  is  on  dead  center:  displacement  of  the  valve  =  the 
steam  lap  +  the  lead. 

Valve  Moved  From  Mid-Travel 
/'Position  By  A  Distance*  Lap  +  Lead 


Direction  Of 
Rotation- 


D  \  A 

Angle  Of  Advance 
FIG.  141.  —  Showing  angle  of  advance  for  an  inside-admission  (piston)  slide  valve. 

152.  The  "Angularity"  Or  "Obliquity"  Of  A  Connecting  Rod 

is  its  ever-changing  angular  position  with  respect  to  the  engine- 
cylinder  axis  line.  At  the  instant  pictured  in  Fig.  142,  it  is  the 
angle  FBD.  When  the  crosshead  is  at  the  end  of  its  stroke 
(Fig.  143,  1)  the  angularity  is  zero.  The  effects  of  connecting- 
rod  angularity  are:  (1)  It  makes  the  average  velocity  of  the 
crosshead  during  the  first  half  of  its  stroke,  on  the  forward  stroke 
(toward  the  shaft)  ,  greater  than  that  during  the  second  half  of  its 
stroke.  (2)  On  the  return  stroke,  angularity  makes  the  average 
velocity  of  the  crosshead  during  the  first  half  stroke  less  than  that 
during  the  second  half.  Since  the  motion  of  a  slide  valve  is  not 
appreciably  affected  by  the  angularity  of  its  connecting 
(eccentric)  rod,1  the  unlike  speeds  of  the  crosshead  during  the 
forward  and  return  strokes  will  tend  to  make  unequal  the 
valve  events  for  the  two  ends  of  the  cylinder.  Thus,  if  any  one 
event,  such  as  cut-off,  were  made  to  occur  at  the  same  fraction 
of  both  the  forward  and  return  strokes,  all  other  events  would 
occur  at  unequal  fractions  of  the  two  strokes. 


102    ST3AM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

•  . .  « 


1  NOTE. — THE  ANGLE,  AT  ANY  INSTANT,  BETWEEN  THE  ECCENTRIC 
ROD  AND  THE  VALVE-STEM  Axis  LINE  WOULD  BE  CALLED  THE  ANGU- 
LARITY OF  THE  ECCENTRIC  ROD.  Now,  since  the  eccentric  rod  is 
ordinarily  of  great  length  as  compared  to  the  throw  of  the  eccentric,  the 
angularity  of  the  eccentric  rod  never  becomes  very  large.  For  small 
angularities  the  effects  explained  above  are  so  small  that  they  may 
practically  be  neglected. 

EXPLANATION. — Fig.  142  is  a  dia- 
gram of  a  crank-and-connecting-rod 
mechanism  of  a  constant-speed  engine. 
The  crosshead,  B,  is  shown  in  the 
middle  of  the  stroke,  AO,  under 
which  condition  the  crank  pin  is 
at  F.  It  is  evident  that,  as  the 
crosshead  completes  the  first  half  of 
its  forward  stroke,  the  crank  pin 
moves  from  Q  to  F.  Also,  as  the 
crosshead  completes  the  last  half 
of  its  stroke,  the  crank  pin  moves 

from  F  to  E.  Thus,  since  the  rotating  speed  of  the  crank  pin  of  a  con- 
stant-speed engine  does  not  vary,  the  average  piston  speed  must  be 
greater  from  A  to  B  than  from  B  to  0.  The  reason  is  that  half  of  the 
stroke,  AO,  has  been  completed  before  the  crank  pin  has  turned  a  quarter 
of  a  revolution;  that  is,  before  the  crank  pin  has  reached  G.  Likewise, 
on  the  return  stroke  (mechanism  is  shown  dotted  on  return  stroke)  the 
crank  pin  turns  from  E  to  H,  or  more  than  a  quarter  revolution,  while 


Mechanism  On 
Return  Stroke-''    Crank,' 
C/rc/e 

FIG.  142. — Showing  position  of  crank 
when  crosshead  is  at  half  stroke. 


Diagram  Of  3 

Yoke  Velocity  ± 

In  Scotch -Yoke  o 

Mechanism 


'Mict-5troke\    .„ 

Position       \  Crosshead 

"Piston  Rod 


'Connecting 
Rod 


"rank-Pin 
Circ/e 
II.  Scotch-Yoke  Mechanism. 


I.  Standard  Crank  Mechanism. 
FIG.  143. — Velocity  diagrams  for  standard  crank  and  scotch-yoke  mechanisms. 

the  crosshead  completes  the  first  half  of  its  return  stroke,  or  O  to  B. 
Furthermore,  the  crank  pin  turns  from  H  to  Q  while  the  crosshead 
completes  the  last  half  of  its  return  stroke,  or  B  to  A.  Hence,  on  the 
return  stroke,  the  average  speed  of  the  piston  from  O  to  B  is  less  than  its 
average  speed  from  B  to  A.  Hence,  it  is  evident  that  even  though  the 
circumferential  speed  of  an  engine  crank  pin  is  constant,  the  average 
speed  of  its  crosshead  will,  because  of  angularity,  be  greater  during  the 
first  half  of  its  stroke  than  during  the  last  half — or  vice  versa. 


SEC.  153]        SLIDE  VALVES  AND  THEIR  SETTING 


103 


NOTE. — THE  VARIATIONS  OF  THE  CROSSHEAD  VELOCITY  DURING  A 
STROKE  may  be  shown  by  plotting  the  velocity  on  a  graph  (Fig.  143,  /). 
It  is  evident  from  this  graph  that  the  crosshead  velocity  during  the  head- 
end part  of  the  stroke  is  greater  than  that  at  corresponding  points  in  the 
crank-end  part  of  the  stroke.  The  Scotch-yoke  mechanism  (Fig.  143,  //) 
gives  a  velocity  diagram  which  does  not  show  such  characteristics.  This 
is  because  there  is  no  angularity  with  this  mechanism. 

153.  "Dead  Center"  denotes  the  position  of  an  engine 
mechanism  (Figs.  144  and  145)  when  the  piston  is  exactly 

..-Direction  Of  Rotation 
X/  ^-— 77—-^  -Crank  Shaft 

//^rs<XQ 


FIG.  144. — Engine  on  head-end  dead  center. 

at  one  end  of  its  stroke.  An  engine  is  evidently  on  dead  center 
when  the  center,  0,  of  its  crank  pin  lies  on  the  cylinder  axis 
line,  CL.  The  two  dead-center  positions  are  termed:  (1) 
Head-end  dead  center,  when  the  piston,  P,  is  at  the  extreme  end 
of  its  stroke  and  nearest  to  the  cylinder  head.  (2)  Crank-end 
dead  center,  when  the  piston,  P,  is  nearest  to  the  engine  crank 

,-Direction  Of  Rotation 
•     0'.- -Crank  Pin 

; Crank  Shaft 

Connecting 


FIG.  145. — Engine  on  crank-end  dead  center. 

shaft  and  at  the  extreme  end  of  its  stroke.  In  making  valve 
adjustments,  it  is  essential  that  one  understands  how  to  place 
the  engine  exactly  on  dead  center.  A  slight  error  in  the  posi- 
tion of  the  crank  shaft  when  the  engine  is  thought  to  be  on  dead 
center  will  introduce  a  relatively  large  error  in  the  position 
of  the  valve,  even  though  the  piston  may  appear  to  be  at  the 
end  of  its  stroke. 


104    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


NOTE. — To  PLACE  AN  ENGINE  ACCURATELY  ON  DEAD  CENTER  BY  THE 
TRAMMEL  METHOD  (Fig.  146)  the  engine  is  turned  by  hand  (or  by 
"barring")  in  the  same  direction  as  that  in  which  it  normally  runs  until 
the  crosshead  is  somewhere  near  the  end  of  its  stroke.  Then  a  mark,  A, 


Scratch 
Marks- 


Scratch  Mark 
On  F/y wheel 

Wire  Trammel' 
FIG.  146. — Illustrating  method  of  finding  the  dead  centers  of  an  engine. 

is  scratched  on  the  crosshead  and  a  mark,  B,  directly  opposite  A,  is 
scratched  on  one  of  the  guides.  Then,  with  the  engine  remaining  in  this 
position,  a  pointed  tram,  C,  (Figs.  146  and  147)  is  placed  in  a  center-punch 
mark  on  the  floor  or  engine  frame  and  a  mark,  D,  Fig.  146,  is  scratched 
with  the  upper  end  of  the  trammel  on  the  engine  flywheel,  as  shown. 
The  trammel  may  be  of  any  reasonable  size  but  usually  it  can  be  worked 

with  most  conveniently  if  its  upper 
end  extends  about  3  ft.  or  less  above 
the  floor  line. 

The  engine  is  now  turned  past  the 
dead  center,  in  the  same  direction, 
until  point,  A,  returns  and  again 
coincides  with  B.  Then  the  mark  E 
is  scratched  on  the  flywheel  with  the 
trammel.  The  distance  DE  is  then 
bisected  (halved)  with  a  pair  of  divid- 
ers and  a  mark,  as  at  F,  is  scratched 
at  the  bisection.  The  engine  is  now 
turned  until  the  point  F,  coincides 
with  the  upper  trammel  point.  The 
engine  is  then  on  one  of  the  dead 
centers  (head-end  dead  center  in 
Fig.  146).  The  other — crank-end — 

dead  center  is  diametrically  opposite  the  one  just  located  at  F.  To  mark 
the  other  dead-center  point  on  the  flywheel,  measure  the  circumference 
around  the  face  of  the  wheel  with  a  steel  tape.  Take  half  the  circumfer- 
ence and  scratch  a  mark,  as  G,  at  the  corresponding  point. 


Point  for 
Scribing  on  Flywheel J 

/Trams  Made  From  Steel  Wire' 
(No.  8  or  Heavier 
Wire  Should  be  Used) 


Point  For  Scribing 
'on  Crank  Disc 


Point  to  be  Set  in  Punch  \l 
Mark  on  Engine  Frame--™ 

Point  to  Set  in  Punch  Mark 

in  Engine  Base  or  Floor --- 


FIG.   147. —  "Trams"  used  in  placing 
engines  on  dead  center. 


SEC.  153]        SLIDE  VALVES  AND  THEIR  SETTING 


105 


If  the  running  direction  is  the  reverse  of  that  indicated  by  the  arrow, 
locate  point  E  before  locating  D.  In  any  case  when  setting  the  engine  on 
center,  after  locating  the  middle  point  F  on  the  wheel,  turn  the  wheel 
backward  through  about  Y±  turn  before  finally  bringing  the  middle  mark 
F  up  to  the  trammel  point. 

NOTE. — A  METHOD  OF  PLACING  AN  ENGINE  ON  DEAD  CENTER  BY 
USING  A  STATIONARY  MARKER  INSTEAD  OF  A  TRAMMEL  is  shown  in 


Direction  Of 
Rotation 


.-Direction  Of 
Rotation 


'Stationary 
Marker 

FIG.  148. — First  position.  The  marker, 
P,  should  be  rigidly  fixed.  Marker  lo- 
cation scribed  on  flywheel  at  D. 


FIG.  149. — Second  position.    Marker  lo- 
cation again  scribed  on  flywheel  at  E. 


Figs.  148,  149  and  150.  This  method  may  be  more  convenient  where 
the  marker,  P,  can  be  fastened  rigidly  to  some  stationary  object  which  is 
adjacent  to  the  flywheel  rim.  The  general  procedure  with  this  is  the 
same  as  with  the  trammel  method  which  is  described  above.  The  refer- 
ence letters  used  in  the  trammel-method  description  also  apply  to  Figs. 
148  to  150. 

NOTE. — A  CONVENIENT  METHOD  FOR  SETTING  A  VERTICAL  ENGINE 
ON  DEAD  CENTER  (Troy  Engine  Co.)  is  illustrated  in  Fig.  151.  Turn  the 
engine  to  near  dead  center.  Mark 
some  point,  P,  on  the  frame  with  a 
center  punch.  With  a  tram  (which 
may  be  a  wooden  stick  having  a  nail 
driven  through  each  of  its  ends)  and 
with  P  as  a  center,  scribe  point  S 
on  the  rim  of  the  wheel.  Spot  an- 
other center-punch  mark,  A,  on  the 
frame.  With  a  pair  of  dividers,  or 
another  tram,  and  with  A  as  a  center, 
scribe  arc  B  on  the  crosshead.  All 
of  the  foregoing  are  shown  in  7. 


FIG.  150. — Third  position.     Engine  on 
dead  center;  mark,  F,  opposite  marker. 


are    shown   in 

Now,  turn  the  engine  through  dead  center  and  until  the  crosshead  returns 
to  its  former  position  (see  //),  the  distance  AB  being  the  same  as  in  7. 
Then  again  with  P  as  a  center1  and  with  the  first-used  tram,  scribe  a  second 
mark  T  on  the  rim  of  the  wheel.  With  dividers  locate  the  point,  C, 
which  is  midway  between  S  and  T.  Turn  the  wheel  until  the  tram  just 
reaches  from  P  to  C,  as  in  777.  The  engine  will  then  be  on  dead  center. 


106     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


CAUTION. — WHEN  SETTING  VALVES,  THE  FLYWHEEL  MUST  ALWAYS 
BE  TURMED  IN  THE  SAME  DIRECTION  to  any  desired  position.  By  so 
doing,  compensation  for  looseness  in  bearings  is  automatically  afforded. 
Thus,  if  the  flywheel  is  accidentally  turned  beyond  some  desired  position, 
it  must  first  be  turned  back  beyond  that  position  and  then  reversed  and 


I- First  Step  E- Second   Step  ffi-Dead   Center 

FIG.   151. —  "Troy"  method  of  setting  an  engine  on  dead  center. 

again  be  turned  forward  to  the  required  position.  If  this  is  not  done, 
there  is  no  assurance  that  the  crosshead  and  piston  occupy  the  proper 
positions  with  respect  to  the  crank. 

154.  An  Accurate  And  Convenient  Method  Of  Setting  An 
Eccentric  "On  Center"  (Figs.  152  and  153)  in  order  to  find  the 

Line  Drawn  By  Nail   .•'! 
In  Templet---., 


.-•Templet 


,  Eccenfr/c-. 


Hub-' 


•Hole  For  Naif 


FIG.  152. — Application  of  templet  in  finding  the  dead  centers  of  an  eccentric. 

two  extreme  positions  of  the  valve  upon  its  seat,  involves 
the  use  of :  (1)  A  templet  as  shown  in  Fig.  152  to  make  a  mark  on 
the  eccentric.  (2)  A  trammel  as  shown  in  Fig.  153  to  make 
marks  on  the  eccentric  strap. 


SEC.  155]        SLIDE  VALVES  AND  THEIR  SETTING 


107 


EXPLANATION. — Place  the  templet  on  the  eccentric  hub  (if  hub  is  not 
machined,  use  the  templet  directly  on  the  shaft)  as  shown  dotted  in 
Fig.  152  and  slide  it  around  the  hub  until  a  nail  inserted  through  the 
hole  in  the  templet  comes  in  contact  with  the  edge  of  the  eccentric,  as  at 
A  and  B.  Then,  using  a  pair  of  dividers  adjusted  by  trial  to  the  proper 
radius,  describe  the  arc,  C,  with  point  A  as  a  center,  and  the  arc,  D,  with 
point  B  as  a  center  so  that  the  arcs  meet  on  the  edge  of  the  eccentric  at  E. 
This  point,  E,  is  then  the  point  of  the  eccentric  farthest  from  the  shaft 
center. 

To  find  corresponding  reference  marks  on  the  eccentric  strap  (Fig.  153) 
a  center-punch  mark,  H,  is  made  at  any  convenient  point  on  the  center 
line  of  the  valve  stem  as  shown.  Holding  one  end  of  the  trammel  in  H, 
the  arcs  S  and  T  are  scribed  with  the  other  end.  Arc  S  and  arc  T  inter- 
sect the  eccentric  edge  at  points  U  and  V  respectively.  Now,  using 
points  U  and  V  as  centers,  arcs  P  and  Q  are  drawn  with  a  pair  of  dividers 


Arc 


Arc 


^..-Trammel 


FIG.   153. — Application  of  trammel  in  finding  the  dead  centers  of  an  eccentric  strap. 

adjusted  to  the  proper  radius  so  that  P  and  Q  intersect  at  the  eccentric 
edge  at  X.  Then  X  is  one  required  reference  mark  on  the  eccentric 
strap.  To  find  the  other  reference  mark  of  the  eccentric  strap,  the  arcs 
R  and  W  are  scribed  from  points  U  and  V  or  from  H.  Then  from  the 
points  G  and  K  where  R  and  W  strike  the  eccentric  edge,  arcs  /  and  J  are 
so  scribed — as  were  P  and  Q — that,  they  intersect  at  the  eccentric  edge  at 
point  Z,  which  is  the  second  reference  mark  on  the  eccentric  strap. 

The  eccentric  is  in  the  " on-center"  position  (the  valve  in  its  extreme 
position)  when  point  E  (Fig.  152)  coincides  with  either  point  X  or  Z 
(Fig.  153).  The  point  E  should  be  marked  on  the  eccentric — and  the 
points  X  and  Z  should,  after  they  have  been  located,  be  marked  on  the 
eccentric  strap — with  a  cold  chisel.  This  will  facilitate  future  adjust- 
ments of  the  valve  and  eccentric. 

155.  The  Setting  Of  Steam-Engine  Valves  or  the  adjusting 
of  the  valve-operating  mechanism  can  be  accomplished  in  two 
ways: 

(1)  By  observing  the  operation  of  the  valve  when  the  cover  is 


108     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


removed  from  its  chest  and  as  the  engine  is  turned  by  applying 
external  force  to  the  flywheel.  This  method  of  setting  valves 
is  frequently  called  setting  by  measurement.  Sometimes  it 
is  possible  to  watch  the  movement  of  the  valve  past  the 
port  edges  and,  in  the  proper  positions,  to  measure  the 
length  of  the  port  opening;  such  valves  may  be  set  by 
direct  measurement.  With  certain  other  engines  these  openings 
must  be  measured  indirectly  (Sec.  156)  or  by  making  templets 
or  working  models  of  the  valve  and  its  seat ;  indirect  measure- 
ment setting  is  necessary  for  these  engines.  Setting  by 
measurement,  because  of  the  many  influencing  factors  in 
steam  engine  operation,  is  not  subject  to  rigid  rules  and, 
therefore,  is  not  sure  to  produce  the  best  results  in  every  case. 
It  is,  on  the  other  hand,  a  relatively  rapid  and  reasonably- 
certain  method  for  setting  slide  valves.  This  method  is 
discussed  in  following  sections. 

(2)  By  studying  steam  engine  indicator  diagrams  taken  from 
the  engine  and  making  changes  which  seem,  after  this  study, 
to  be  necessary.  This  method  requires  a  thorough  under- 
standing of  the  relations  between  the  valve  mechanism  and 
the  indicator  diagram,  which  is  treated  fully  in  Div.  3.  This 

method  is  likely  to  be 
slow  and  cumbersome  at 
first  trial.  But,  after 
some  experience,  one 
learns  to  set  the  valves 
quite  rapidly.  It  is  the 
only  method,  however, 
which  insures  certainty 
of  valve  adjustment.  It 
should,  therefore,  be  used 
to  check  the  final  setting 
of  all  valves  even  when  a  preliminary  setting  has  been  made  by 
measurement. 

156.  The  "Indirect-Measurement"  Method  of  Ascer- 
taining Valve  Operation  must  be  employed  whenever  the 
valve  ports  are  not  accessible  for  direct  observation.  As 
piston  valves  are  generally  of  the  inside-admission  type, 
they  are  the  ones  to  which  this  method  is  most  often  applied. 


Inside  Admission   .--Steam 
Valve- .waft    >.-''w* Space 


\  'Cylinder  Port  Cylinder  Por  f  - ' 

^'Exhaust  Space 

FIG.  154. — Illustrating  method  of  setting  an 
inside-admission  valve  where  the  cylinder  ports 
are  not  accessible. 


SEC.  157]        SLIDE  VALVES  AND  THEIR  SETTING 


109 


The  method  is  explained  below.  See  also  the  example  under 
Sec.  167  wherein  the  setting  of  a  piston  slide  valve  by  an  indi- 
rect method  is  described. 

EXPLANATION. — After  the  valve-chest  cover  is  removed  some  line,  such 
as  A,  Fig.  154,  is  selected  as  a  reference  point,  from  which  measurements 
are  to  be  taken.  The  line,  A ,  must  be  so  chosen  that  it  will  not  be  covered 
by  the  valve  at  any  time  during 
its  motion.  The  distances,  AB 
and  AE,  are  then  measured  ac- 
curately with  a  steel  scale  while 
the  valve  is  removed  from  the 
chest.  Also  the  lengths  of  the 
valve  from  C  to  F  and  from  C  to 
D  are  measured.  The  valve  may 


What  Lead?^  p- 8 "- >j 


"Valve  Seat 


"Piston  Valve 


FIG.  155.- 


Finding  lead  by  indirect  measure- 
ment. 


then  be  replaced  into  the  seat. 

The  edges  F  and  B  of  the  valve 

and  seat  may  then  be  placed  to 

coincide  by  moving  the  valve  until  the  distance  from  A  to  C  or  AC  = 

AB  —  CF.     Likewise  the  edges  D  and  E  will  coincide  when  AC  =  AE  — 

CD.     The  exact  opening  of  the  cylinder  port  at  any  time  can  also  be 

determined  by  similar  measurement  to  the  face,  C,  of  the  valve. 

EXAMPLE.— If  (Fig.  155)  AB  =  8  in.,  CF  =  2±i  in.,  and  when  the 
engine  is  on  dead  center  AC  measures  5^  in.,  what  is  the  lead?  SOLU- 
TION.—Obviously,  the  lead  =  8  -  (5^  +  2>£)  =  '8  -  7%  =  H  in. 


'Piston  Valve 


Reference  Edge 
,-'  on  Va/ve  Seat 


Cut  A 


Reference 
Mark  on 
Board 
I- Accessible  Valve 


by  Measuring 
from  Reference 


'Cut  Along  Dotted  Lines 
H- Inaccessible  Valve  Seat 

FIG.  156. — Showing  methods  of  making  templets  of  valves  and  seats.  (Whenever 
the  templet  material  can  be  placed  against  the  valve  or  seat,  use  the  method  at  the 
left.  Templets  of  inaccessible  seats  are  made  as  shown  at  the  right.) 

157.  The  Templet  Method  Of  Ascertaining  Valve  Opera- 
tion is  a  modification  of  the  indirect-measurement  method. 
Templets  (Fig.  156),  or  full-size  working  models,  of  the  valve 
and  its  seat  are  cut  from  thin  material  such  as  sheet  metal, 
cardboard,  or  thin  wood.  Templets  of  inaccessible  valve  seats 
must  be  made  from  measurements.  Templets  of  valves  and 


110    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

accessible  seats  may  be  made  by  placing  the  templet  material 
with  its  edge  against  the  valve  or  seat  (Fig.  156, 1),  and  marking 
the  working  edges  directly  from  the  valve  or  seat.  After  the 
templets  are  made,  the  valve  may  be  replaced  in  its  chest  and 
set  into  its  midtravel  position  (Fig.  157)  either  by  direct 


Templet 

Of  Piston    tffD;v;ders 


-Board  Kept  Near  Engine 
For  Use  In  Setting  Valves      • 


' -Templet  Of  Valve 

Seat  Tacked  To  Board 


Center  Punch.  . ' 
Marks    p  •  •-•'" 


I-  Position  Of  Templets         H-Position  Of  Valve  In  Seat 
FIG.  157. — Method  of  establishing  marks  for  setting  a  slide  valve  with  templets. 

observation  or  by  indirect  measurement.  In  this  position 
the  laps  at  the  two  ends  of  the  valve  should  be  equal.  The 
valve-seat  templet  is  then  tacked  to  a  board  and  the  valve 
templet  placed  against  it  (Fig.  157,  7)  in  the  same  relative 
position  as  the  valve  in  the  seat.  Punch  marks,  P,  are  then 


-  Dividers 


I"  Position  Of  Templets 


Position  Of  Valve  In  Seat 


Fia.   158. — Method    of    determining    lead    when    setting    a    slide    valve  by    means  of 

templets. 

made  on  the  valve  chest  and  the  valve  rod  a  convenient 
distance  apart  (4  in.  in  Fig.  157,  II).  Similar  marks,  M, 
are  made,  as  shown,  on  the  valve  templet  and  on  the  board. 
Once  these  templets  have  been  made  and  marked,  future 


SEC.  158]        SLIDE  VALVES  AND  THEIR  SETTING 


111 


valve  adjustments  can  be  effected  without  removing  the  valve 
chest  cover.  Likewise  (Fig.  158),  the  position  of  the  valve 
upon  its  seat  can  be  determined  at  any  instant — as,  for 
instance,  during  adjustment — simply  by  making  equal  the 
distances,  X,  between  the  two  pairs  of  marks.  See  also  the 
example  under  Sec.  167  which  describes  how  wooden  battens 
may  be  used  instead  of  templets. 

158.  Adjustment  Of  A  Slide -Valve  Mechanism  Can  Be 
Effected  In  Only  Two  Ways :  (1)  By  changing  the  position 
of  the  eccentric  on  the  crank  shaft,  thus  changing  the  angular 
advance  of  the  eccentric.  (2)  By  changing  the  position  of  the 
valve  upon  its  seat  for  any  eccentric  position.  This  is  done  by 
altering  the  total  length  from  the  eccentric  center  to  the  valve, 


Vafve-Stem 
Adjusting  Nuts, 

Lock  /:      Lock- 


Guide.. 


Stem. 


•-Locknut      Piston 
'  '7/1 


Valve  Adjusting 


'"Eccentric  Oil  Va/ve-Stem  \ 

Rod  Reservoir     Slider  Or  Block--' 

FIG.  159.  —  Valve-stem  adjustment 
at  the  valve-stem  slider.  (Chuse  engine 
&  Mfg.  Co.) 


FIG.    160.— -Method    of    adjusting 
stem  length  at  valve. 


as  measured  along  the  valve  mechanism,  that  is,  by  changing 
the  effective  length  of  the  valve  stem.  Evidently,  this  length 
can  be  changed  by  altering  either  the  distance  from  the  eccen- 
tric center  to  the  valve  block,  or  the  distance  from  the  block 
to  the  valve.  Each  of  these  distances  may,  with  certain 
engines  be  altered  at  either  of  the  two  ends  of  the  rods  which 
maintain  the  distances.  On  other  engines,  adjustment  is 
provided  only  at  one  end  of  the  valve  stem  or  eccentric  rod 
or  at  one  end  of  each.  Figs.  159  and  160  show  means 
provided  for  this  adjustment. 

NOTE. — IN  MOST  SHAFT-GOVERNED  ENGINES  THE  ANGLE  OF  ADVANCE 
CANNOT  BE  ADJUSTED,  that  is — the  eccentric  position  is  fixed  by  the 
governor.  In  these  engines  the  valve  is  obviously  only  adjustable  by 
altering  the  effective  length  of  the  eccentric  rod  and  valve  stem. 


112    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


159.  Table  Showing  Effects  On  the  Steam-Engine  Cycle 
Of  Slide-valve  Adjustments  For  The  Outside -admission 
Slide  Valve. 


Adjustment 

End  of 
cylin- 
der 

Effect  on  valve  events 

Admis- 
sion 

Cut-off 

Release 

Com- 
pression 

Valve-stem  effective  length 

Lengthened 

Head 

Later 

Earlier 

Earlier 

Later 

Crank 

Earlier 

Later 

Later 

Earlier 

Shortened 

Head 

Earlier 

Later 

Later 

Earlier 

Crank 

Later 

Earlier 

Earlier 

Later 

Angular  advance  of  eccentric 

Increased 

Head 

Earlier 

Earlier 

Earlier 

Earlier 

Crank 

Earlier 

Earlier 

Earlier 

Earlier 

Decreased 

Head 

Later 

Later 

Later 

Later 

Crank 

Later 

Later 

Later 

Later 

NOTE. — To  USE  THE  ABOVE  TABLE  FOR  INSIDE-ADMISSION  VALVES 
bear  in  mind  that:  (1)  Effects  of  changing  effective  valve-stem  length  are 
opposite  to  those  given  in  the  table.  (2)  Effects  of  changing  the  angular 
position  (advance)  of  the  eccentric  are  the  same  as  for  outside  admission 
slide  valves.  It  must  not  be  forgotten,  however,  that  for  inside-admission 
valves  (Sec.  151)  the  angle  of  advance  is  measured  in  the  direction  of 
rotation  from  a  line  90  deg.  behind  the  crank  position  to  the  line  of  the 
eccentric  position. 

160.  In  Setting  The  Valves  Of  A  New  Engine,  before  putting 
the  engine  into  operation,  do  not  at  first  change  or  disturb 
any  adjustments  of  the  valve  mechanism.  Remove  the  steam- 
chest  cover  and,  turning  the  engine  by  hand,  watch  the  motion 
of  the  valve  upon  its  seat.  With  piston- valve  engines  the 
indirect-measurement  method  (Sec.  156)  must  be  employed. 
Valve  and  seat  dimensions  may  be  obtained,  without  removing 
the  valve  from  its  seat,  by  consulting  the  engine-maker's 
blueprints.  If,  upon  examination  of  the  valve  action  with  the 
cover  removed,  it  is  thought  probable  that  the  engine  will  run 
with  the  existing  adjustment,  replace  the  cover  and  start  the 
engine.  If  desirable,  the  engine  may  be  started  without  first 
examining  the  valve  operation,  as  no  harm  can  result  even  if 
the  valves  are  not  properly  set.  Then  equip  the  engine  with 


SEC.  161]        SLIDE  VALVES  AND  THEIR  SETTING  113 

indicators  and  take  cards  first  under  no  load  and  then  with 
gradually  increasing  loads.  Engine  builders  usually  carefully 
adjust  the  valves  for  their  correct  operation  before  shipping 
an  engine.  If,  however  (Sec.  112)  the  indicator  diagrams 
reveal  faulty  valve  motion  and  not  until  then  it  may  be  con- 
cluded that  adjustment  is  necessary.  The  adjustment  should 
be  made  in  accordance  with  builder's  instructions.  If  these 
instructions  were  not  sent  with  the  engine,  they  should  be 
procured  by  writing  to  the  factory.  If  valves  must  be  set 
without  specific  instructions  from  the  engine  makers,  the 
methods  of  succeeding  sections  may  be  employed. 

161.  In  Setting  The  Valves  Of  An  Old  Engine,  it  is  advisable 
to  procure  the  manufacturer's  instructions,  if  possible,  and  then 
to  make  the  adjustments  as  recommended  by  the  manu- 
facturer.    If  it  is  impossible  to  obtain  factory  instructions, 
the  valve  may  be  set  as  hereinafter  explained. 

162.  All  Slide  Valves  May  Be  Set  For  One  Of  Three  Con- 
ditions, any  of  which  may  give  satisfactory  operation.     The 
ideal  setting  of  engine  valves  is  not  attainable  with  a  single 
valve  because  of  the  angularity  of  the  connecting  rod  (Sec. 
152).     The  setting  of  a  slide  valve  must,  therefore,  be  a  com- 
promise.    The  valve  may  be  set  for:  (1)  Equal  leads  at  both 
ends  of  the  stroke.     This  setting  will  make  all  events,  especially 
cut-off,  unequal  for  the  two  ends  of  the  cylinder.     (2)  Equal 
cut-offs,  in  per  cent  of  stroke,  during  the  forward  and  return 
strokes.     This  setting  will  make  all  of  the  other  events  unde- 
sirably unequal  for  the  two  ends  of  the  cylinder.     (3)  Inter- 
mediate between  equal  leads  and  equal  cut-offs.     By  setting  an 
engine  for  more  lead  at  the  crank  end  of  the  stroke  than  at  the 
head  end,  the  cut-offs  are  made  more  nearly  equal  for  the 
forward  and  return  strokes.     Setting  slide  valves  for  each 
of  these  conditions  will  be  discussed  separately  in  following 
sections.          v 

163.  The  Firs'f  Step  In  Setting  Any  Slide  Valve  Is,  therefore, 
to  decide  whether  it  is  to  be  set  for:  (1)  Equal  leads.     (2) 
Equal  cut-offs.     (3)  Intermediate  between  equal  leads  and  equal 
cut-offs.     It  really  makes  little  difference  which  condition  is 
selected.     An  engine  will  probably  operate  most  quietly  when 
set  for  equal  leads.     When  set  for  equal  cut-offs,   it  will 
probably  operate  most  economically.     A  setting  intermediate 


114    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

between  (1)  and  (2)  provides  reasonably  quiet 'operation  and 
good  economy.  But,  in  any  case,  the  difference  in  the 
operating  results  obtained  from  any  of  the  three  methods  of 
setting  is  usually  very  small.  Therefore,  since  setting  for  equal 
leads  is  the  easiest  of  the  three,  this  condition  is  usually  sought 
by  operating  engineers  and  is  frequently  recommended  by 
engine  builders,  especially  for  small  engines.  For  large  engines 
condition  (3)  above  is  usually  recommended.  For  vertical 
engines,  the  lead  on  the  top  or  head  end,  is  usually  considerably 
less  than  on  the  bottom  end  because  the  cut-offs  are  so  more 
nearly  equalized  and  because  the  weight  of  the  reciprocating 
parts  acts  against  the  steam  pressure  on  the  up  stroke. 
Checking  valve  settings  with  an  indicator  is  always  the  safest 
method  of  determining  the  proper  leads  for  any  given  engine. 
164.  In  Setting  A  Slide  Valve  For  Equal  Leads  One  Must 
First  Decide  Whether  It  Is  To  Be  Set  For  "Design-Deter- 
mined Equal  Leads"  Or  For  "Selected  Equal  Leads."— By 
design-determined  equal  leads  is  meant  equal  leads,  be  their 
amount  what  it  may,  the  dimension  of  which  was  pre-deter- 
mined  by  the  designer  of  the  engine  and  for  which  the  angular 
advance  of  the  eccentric — or  its  equivalent — has  been  per- 
manently fixed.  Hence,  setting  a  slide  valve  for  design- 
determined  equal  leads  involves  only  changing  the  valve- 
stem  or  eccentric-rod  effective  length  until  the  leads  at  both 
head  and  crank  end  are  equal.  To  alter  the  amount  of  the 
equal  leads  which  was  thus  predetermined  and  fixed  by  the 
designer  of  the  engine,  would  necessitate  changing  the  angular 
advance  of  the  eccentric  on  the  engine  shaft.  This  would 
necessitate  the  cutting  of  a  new  shaft  keyway  or  otherwise 
making  mechanical  changes  in  the  engine  which  would  involve 
more  work  than  mere  adjustments.  By  selected  equal  leads 
is  meant  equal  leads  the  dimension  of  which  is  selected,  by 
following  a  rule  (as,  for  example,  that  of  Sec.  165)  by  the 
person  who  is  setting  the  valve.  Setting  for  selected  equal 
leads  probably  involves  not  only  changing  the  valve-stem  or 
eccentric-rod  effective  length  but  also  changing  the  angular 
advance  of  the  eccentric. 

NOTE. — IN  SETTING  THE  VALVE  OF  A  SHAFT-GOVERNED  ENGINE  IT  Is 
USUALLY  DESIRABLE  To  SET  FOR  DESIGN-DETERMINED  EQUAL  LEADS 
rather  than  for  selected  equal  leads.  As  explained  in  Sec.  158,  the  eccen- 


SEC.  165]        SLIDE  VALVES  AND  THEIR  SETTING  115 

trie  of  a  shaft-governed  engine  is  not  adjustable  on  the  engine  shaft. 
Hence,  it  is  impossible,  with  an  engine  of  this  type  to  set,  the  valve  for 
equal  leads  other  than  the  "design-determined"  lead  for  which  the  valve 
gear  and  governor  was  originally  designed,  without  changing  the  position 
of  the  flywheel  on  the  shaft.  This  will  ordinarily  necessitate  the  cutting 
of  a  new  keyway  in  the  shaft. 

NOTE. — IT  Is  SELDOM  ADVISABLE  To  SHIFT  THE  ECCENTRIC  (FLY- 
WHEEL), OF  A  SHAFT-GOVERNED  ENGINE,  ON  THE  ENGINE  SHAFT. 
This  may  appear  to  be  necessary  when  it  really  is  not,  due  to  the  governor 
being  out  of  adjustment.  See  Div.  7  concerning  shaft-governor  adjust- 
ment. The  eccentrics,  and  flywheels  of  shaft-governed  engines  are 
carefully  located,  in  relation  to  the  shaft,  by  their  manufacturers  before 
the  engine  leaves  the  factory.  It  is  therefore  seldom  indeed  that  the 
shifting  of  the  flywheel — which  will  necessitate  the  cutting  of  a  new 
keyway  in  the  shaft — is  justified.  If,  after  the  governor  has  been  correctly 
adjusted,  and  the  leads  are  still  of  incorrect  amount,  then  it  may  be 
necessary  to  shift  the  eccentric — fix  the  flywheel  to  the  shaft  in  a  new 
position. 

165.  The  Proper  Lead  For  Any  Slide  Valve  should,  finally, 
be   determined   with   an  indicator    (Sec.    175).     In   general, 
the  lead  may  be  set  at  about  J^2  m-  for  each  foot  of  stroke — 
but  it  is  seldom  in  any  case  that  the  lead  should  be  much  less 
than  3^2  m-  That  is,  an  engine  which  has  a  12-in.  stroke  should 
have  a  ^2~m-  lead.     One  which  has  a  24-in.  stroke  should 
have  a  JJLG  m-  lead  and  so  on.     If  the  selected  lead  is  not  the 
correct  one  for  the  engine,  the  indicator  will  reveal  the  remedy. 

166.  The  Procedure  To  Be  Followed  In  Setting  Plain  Slide 
Valves  For  Equal  Leads   is  specified  in  Table   167.     This 
table  applies  only  to  plain  "D"  or  to  plain  piston  slide  valves; 
it  does  not  apply,  directly  to  riding-cut-off  valves,  for  which 
see   Sec.    172.     See   preceding  sections  for  definitions  of  the 
terms  " design-determined  equal  leads"  and  " selected  equal 
leads."     Always,  when  setting  valves,  turn  the  flywheel  or 
the  eccentric  in  the  same  direction,  preferably  in  the  direction 
in  which  they  will  move  when  the  engine  in  running;  see 
Sec.  153.     Note  that  by  changing  the  valve-stem  — or  eccentric 
rod— effective  length,  the  leads  at  both  head  and  crank  ends 
may    be    made    equal.     When    the   valve    opens   an   equal 
amount   at   each   end,   the   eccentric   rod  and  valve  rod  are 
then  of  correct  length  for  equal  leads.     By  shifting  the  eccen- 
tric on  its  shaft — changing  its  angular  advance — the  amounts 
of  the  equal  leads  may  be  altered. 


116    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


167.  Table  Showing  Procedure  To  Be  Followed  In  Setting 
Plain  Slide  Valves  For  Equal  Leads. — Read  carefully  the 
preceding  section. 


Operation 

Steps  to  be  taken 

Engine  has  a  throttling 
governor 

Engine  has  a  shaft 
governor 

Identifying  letter 

What  to  do 

Eccentric  is 
keyed  to 
shaft 

Eccen- 
tric is 
not 
keyed 
to  shaft 

Flywheel  is 
keyed  to 
shaft 

For 
design- 
deter- 
mined 
equal 
leads 

For 
selected 
equal 
leads 

For 
selected 
equal 
leads 

For 
design- 
deter- 
mined 
equal 
leads 

For 
selected 
equal 
leads 

I 

1 

II 
| 

1 

III 

1 

IV 
? 

1 

V 

1 

VI 

0) 

> 
1 

VII 

1 

'(3 

> 

0 

Indirect  valve  £j 

IX 

E 

1 
•8 
£ 
5 

Indirect  valve  X 

1 

s 

Indired 

1 

5 

| 

! 

1 
Q 

Indired 

A 

Select  equal  lead  dimension 
for  which  valve  will  be  set, 
Sec.  165. 

'• 

1 

i 

1 

1 

1 

•  • 

•• 

i 

1 

B 

Establish  dead  centers  and 
mark  on  flywheel,  Sec.  153 

1 

2 

2 

2 

2 

i 

1 

2 

2 

C 

Remove  valve-chest  cover  or 
covers 

2 

2 

3 

3 

3 

3 

2 

2 

3 

4 

3 
4 

D 

Block  shaft  governor  to  nor- 
mal operating  position,  Sec. 

•• 

E 

Remove  valve,  measure  it  and, 
if  desirable,   make  templet, 
Sec.  157. 

•• 

3 

4 

4 

•• 

3 

•• 

5 

F 

Measure  the  valve  seat  and, 
if  desirable,  make  templet, 
Sec.  157. 

•• 

4 

5 

5 

4 

•• 

6 

G 

Replace  valve  on  seat  and 
connect  it  in  proper  running 
order  to  its  valve  stem. 

5 

•• 

6 

6 

5 

7 

H 

Turn  engine  crank  to  its  head- 
end dead-center  position, 
Sec.  153. 

3 

6 

4 

7 

•• 

3 

6 

5 

8 

I 

Loosen  eccentric  and  rotate  it 
on  its  shaft  to  extreme  head- 
end position,  Sec.  154. 

•• 

4 

7 

•• 

•• 

•• 

J 

Measure  accurately  the  lead 
or  port  opening  at  this  end. 
Call  it  Li. 

4 

7 

5 

8 

5 

8 

4 

7 

6 

9 

K 

Rotate  the  eccentric  to  the 
extreme  crank-end  position, 
Sec.  154. 

•• 

•• 

•• 

•• 

6 

9 

•• 

•• 

•• 

•• 

SEC.  167]        SLIDE  VALVES  AND  THEIR  SETTING 


117 


Steps  to  be  taken 

Engine  has  a  throttling 
governor 

Engine  has  a  shaft 
governor 

Identifying  letter 

What  to  do 

Eccentric  is 
keyed  to 
shaft 

Eccen- 
tric is 
not 
keyed 
to  shaft 

Flywheel  is 
keyed  to 
shaft 

For 
design- 
deter- 
mined 
equal 
leads 

For 
selected 
equal 
leads 

For 
selected 
equal 
leads 

For 
design- 
deter- 
mined 
equal 
leads 

For 

selected 
equal 
leads 

Direct  valve  >-> 

Indirect  valve  K 

III 
I 

1 

5 

Indirect  valve  ^ 

Direct  valve  <« 

Indirect  valve  ^ 

Direct  valve  ^ 

Indirect  valve  S 
H 

IX 
E 

! 

1 

Indirect  valve  ^ 

L 

Turn  engine  crank  to  its 
crank-end  dead-center  posi- 
tion, Sec.  153. 

5 

S 

6 

9 

•• 

•• 

5 

8 

7 

10 

M 

Measure  the  lead  or  port 
opening  at  this  crank  end. 
Call  it  Li. 

6 

9 

7 

10 

7 

10 

6 

9 

8 

11 

N 

Calculate   the  difference  be- 
tween Li  and  Lz. 

7 

10 

8 

11 

8 

11 

7 

10 

9 

12 
13 

O 

So    change    the    valve-stem, 
effective  length  that  the  lead 
Z/3  will  be  equal  at  both  head 
and  crank  ends,  that  is,  so 
that  Z/3  =  (Li  +  L2)/2:  The 
valve-stem   effective   length 
must  be  changed  by  J^  the 
difference  between  L\  and  L2, 
which  was  found  in  N.     See 
Sec.     166,   the     note    below 
and  the    following    examples. 
This    should    complete    the 
valve  adjustment  for  design- 
determined  equal  leads. 

8 

11 

9 

12 

9 

12 

8 

11 

10 

P 

Turn  engine  crank  to  its 
crank-end  dead-center  posi- 
tion. 

•• 

•• 

10 

13 

10 

13 

Q 

Rotate  the  eccentric  on  the 
shaft  to  change  the  lead  to 
the  selected  dimension,  as 
selected  in  A. 

•• 

11 

14 

11 

14 

14 

R 

Fasten  the  eccentric  securely 
to  the  engine  shaft  in  this 
new  position,  Sec.  164. 

- 



12 

15 

12 

15 



•• 

8 

Rotate  flywheel  on  shaft  to 
change  the  lead  to  the  re- 
quired dimension. 

- 

11 

118     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


Operation 

Steps  to  be  taken 

Engine  has  a  throttling 
governor 

Engine  has  a  shaft 
governor 

Identifying  letter 

What  to  do 

Eccentric  is 
keyed  to 
shaft 

Eccen- 
tric is 
not 
keyed 
to  shaft 

Flywheel  is 
keyed  to 
shaft 

For 
design- 
deter- 
mined 
equal 
leads 

For 
selected 
equal 
leads 

For 

selected 
equal 
leads 

For 

design- 
deter- 
mined 
equal 
leads 

For 
selected 
equal 
leads 

I 

E 

1 

Q 

Indirect  valve^S 

III 

\ 

B 

£ 

5 

Indirect  valve  ^ 

V 

1 
Q 

Indirect  valve  ^ 

Direct  valve  ^ 

Indirect  valve  £ 

IX 

<o 

1 
Q 

E 

1 

•3 

q 

T 

Fasten  governor  flywheel  tem- 
porarily, but  securely,  to 
engine  shaft  in  new  position. 

•• 

12 

15 

12 

13 
14 

16 
17 

13 

14 
15 

16 
17 

U 
V 

For  a  check,  turn  engine 
crank  to  its  head-end  dead- 
center  position  and  measure 
the  lead  at  this  end  also. 

9 

13 

14 
15 

9 
10 

12 

13 

16 

17 

18 

If  the  leads  at  the  two  ends 
are  not  equal,   repeat  such 
steps  as  you  took,  between  H 
t'o    T    inclusive,    until     the 
leads  are  equal  at  both  ends' 
This  step  should  be  unnec- 
essary.    This    repetition    is 
made  necessary  only  by  care- 
less  adjustment   or   by    the 
insecure  fastening  of  a  part 
after  adjustment. 

10 

13 

14 
15 

w 

Replace  valve  chest  cover  or 
covers. 

11 

18 

18 

11 

14 

X 

Check  your  valve  setting  with 
an  indicator;  see  Sec.  175. 

12 

15 

16 

19 

16 

19 

12 

15 

16 

19 

Y 

Cut  new  eccentric  key-way  in 
the  engine  shaft,  if  necessary, 
for  a  permanent  attachment 
and  key  eccentric  thereto  in 
the  new  position. 

•• 

17 

20 





Z 

Cut  new  governor  flywheel 
keyway  in  engine  shaft  in 
new  position  if  necessary  for 
a  permanent  attachment  and 
key  flywheel  thereto;  see 
Sees.  164  and  174. 

17 

20 

A 

Make  valve-setting  reference 
tram  and  spot  tram-refer- 
ence marks  on  valve  stem 
and  stuffing  box.  These  are 
to  insure  rapid  future  reset- 
ting of  the  valve. 

13 

16 

18 

21 

17 

20 

13 

16 

18 

21 

SEC.  167]        SLIDE  VALVES  AND  THEIR  SETTING 


119 


NOTE. — IF  THE  STEAM  PORT  Is  OPENED  MORE  IN  THE  SECOND 
DEAD-CENTER  POSITION  THAN  IN  THE  FIRST,  it  is  an  indication  this 
applies  only  to  direct  or  outside  admission  valves)  that  the  valve  stem 
too  long  and  that  it  must  be  shortened  by  K  the  difference  in  the 
the  amounts  of  the  leads.  //  the  lead  is  less  in  the  second  dead-center  posi- 
tion than  in  the  first  or  if  the  steam  port  is  not  uncovered  at  all,  the  valve 
stem  is  too  short  and  must  be  lengthened;  thus:  (a)  if  the  steam  port  is 
opened,  the  valve  stem  must  be  lengthened  by  %  the  difference  between 
the  leads  at  the  two  ends;  (&)  if  the  steam  port  is  not  opened,  the  valve 
stem  must  be  lengthened  by  K  the  amount  by  which  the  valve  falls  short 
of  opening  it  plus  K  the  lead  at  the  first  dead-center  position.  After  the 
valve  stem  has  been  lengthened  by  the  correct  amount  as  directed  in  (6) 
the  valve  may  not  show  any  lead  at  all. 

EXAMPLE. — SETTING  THE  VALVE  OF  A  THROTTLING-GOVERNED 
PLAIN-INDIRECT-VALVE  (PISTON-VALVE)  ENGINE  FOR  SELECTED  EQUAL 


Tapped  Hole  For 
Steam -Supply  Pipe-. 


Steam  Inlet- 
Ports-. 


Cylinder  Casting--      imaginary 

Position  Of  Piston 

FIG.  161.  —  Showing  how  a  combination 
square  and  blade  are  used  for  making  indi- 
rect measurements. 


Valve- Seat  Liner  Or  Bushing 

FIG.  162.  —  First  adjustment  of 
square — blade  end  against  inner  edge 
of  steam  port. 


LEADS.  ECCENTRIC  Is  NOT  KEYED  To  SHAFT.  Follow  the  steps  of 
Column  VI,  Table  167.  The  exhaust  ports  are  not  shown  in  any  of  the 
illustrations  in  this  example.  (1)  Select  the  equal  lead,  which  will  be 
designated  by  "L8,"  for  which  you  wish  to  set  the  valve,  as  directed  in 
Sec.  165;  assume  that  it  is  to  be  ^2  in.  (2)  Establish  and  mark  the 
dead-center  position  on  the  engine  flywheel  as  directed  in  Sec.  153. 

(3)  Remove  the  valve-chest  covers.  (4)  Remove  the  valve  and  meas- 
ure the  length,  V,  as  shown  in  Fig.  161,  of  the  piston;  say  it  is  2^  in. 

(5)  Measure  with  a  combination  square,  as  shown  in  Fig.  162,  the 
distance  to  the  inner  edge  of  the  steam  port.  Call  the  distance  M ;  say  it 
is  4^  in.  If  the  steam  chest  is  not  alike  at  both  ends,  measure  similarly 
and  record  the  corresponding  distance  M  for  the  other  end  of  the  chest. 
(6)  Replace  the  valve  in  its  seat  and  connect  it  in  proper  running  order 
to  its  valve  stem;  the  valve  stem  will  be  adjusted  to  proper  effective 
length  in  the  next  steps. 

(7)  Loosen  the  eccentric  and  rotate  it  on  the  engine  shaft  to  its  extreme 
head-end  position  as  shown  in  Fig.  163;  see  Sec.  154.  It  is  desirable 


120    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


that,  in  this  step,  the  steam  port  be  opened  wide  as  the  only  object  of  the 
step  is  to  insure  that  the  valve  opens  both  the  head-end  and  the  crank- 
end  ports  by  equal  amounts.  (8)  The  amount,  or  its  equivalent,  by 
which  the  head-end  port  is  opened  is  determined  by  indirect  measurement 


,  Valve 
Stem 


Engine 
Steam  Passages  Shaft-- 

FIG.   163. — Eccentric  in  head-end  extreme  position. 

thus :  The  eccentric  being  in  its  extreme  head-end  position,  as  in  Fig.  163, 
set  the  combination  square  as  shown  in  Fig.  164  and  measure  the  distance 
N',  say  it  is  %  in.  Then,  at  this  head  end,  the  port  opening,  L\  =  M 
-  (N  +  F)  =  4%  -  (H  +  23^)  =  4H  -  2J6  =  1%  in.,  as  shown  in 
Fig.  164. 


LI  'Equivalent/ 
Port  Opening 


FIG.  164. — Measuring  Li  for  head  end;  Li  =  M  -  (N  +  F). 

(9)  Rotate  the  eccentric  on  the  engine  shaft  to  its  extreme  crank-end 
position,  as  shown  in  Fig.  165.  (10)  Measure  the  lead,  Z/2,  for  this  crank 
end  by  the  same  indirect  method  as  that  which  was  used  for  the  head  end. 
If  this  L2  happens  to  be  the  same  amount  as  LI,  the  leads  are  equal  at 


:Steam  Ports  Open 

:          ..-Tapped  Hole  For 

'        /   Steam  Supply  Pipe 


Guide 
/'Block 


Eccentric-' , 
FIG.  165. — Eccentric  in  crank-end  extreme  position. 

both  ends  which  shows  that  the  valve-stem  effective  length  is  correct. 
But  if  they  are  not  equal,  the  valve-stem  length  will  have  to  be  changed. 
Assume  that,  in  this  example,  the  crank-end  port  opening,  L2,  is  found  to 
measure  1^  in.  (11)  Then,  to  be  equal  at  each  end,  the  openings  must 


SEC.  167]        SLIDE  VALVES  AND  THEIR  SETTING  121 

be     changed     to    L3  =  (Li  +  L2)/2  =  (1%  +  1>£)  -5-  2  =  3,Vg  -*•  2  = 


(12)  To  make  the  openings  l^fe  in.  at  each  end,  the  valve-stem  effective 
length  must  be  changed  by  an  amount  equal  to  half  the  difference  between 
Li    and   Li  =  (1%-W)  +2  =H  +2  =  KG    in.     If    the  head-end 
port  is  opened  the  widest,  the  valve-stem  should  be  shortened — if  there 
is    no    rocker    arm    in  the  valve 

mechanism.  If  the  crank-end  port 
is  opened  furtherest,  then  the  valve- 
stem  length  should  be  lengthened. 
After  the  valve-stem  effective 
length  has  thus  been  changed  by 
K 6  in.,  then  its  length  insures 
that  the  crank-end  and  head- 
end steam  ports  will  always  have 
equal  leads;  this  regardless  of  the 
amount  of  the  selected  lead,  the 
setting  for  which  is  made,  in  the 
second  step  following,  by  crank- 
ing the  angle  of  advance  of  the 

eccentric.  FlG    166— Setting  piston  valve  for  selected 

(13)  Turn  the  engine  to  its  crank-  lead.    P  =  M  -  (V  +  L.). 
end  dead-center  position.     (14) 

Change  the  angle  of  advance  so  that  the  equal  lead  at  both  crank  and 
head  ends  will  be  the  selected  lead,  Ls  =  ^2  in.  Proceed  thus:  Set  the 
combination  square,  as  shown  in  Fig.  166,  so  that  the  extending  por- 
tion of  the  blade,  P  =  1%  in.  That  is,  from  Fig.  166,  P  =  M 
-  (V  +  Ls)  =  4>£  -  (2%  +  YZZ)  =  4K  -  2^2  =  13^2  in.  Rotate 
the  eccentric  on  its  shaft  to  the  crank-end  extreme  position,  as  shown  in 
Fig.  163.  Place  the  extending  blade  of  the  combination  square,  which  has 
been  set  at  I3 3^2  in.  as  just  described,  into  the  valve  cylinder  as  shown  in 
Fig.  167.  Rotate  the  eccentric  on  its  shaft  in  the  direction  the  engine  is  to 


' Selected 
Lead 


/Cylinder  Casting 
'  --Piston  Valve 


Position  Of  Crank^ 


Lock  Nut— " 
'Comb/nation Square  Eccentric  Strap • ' ' 

FIG.  167. — Head-end  port  opened  to  the  extent  of  the  lead. 

run  until  the  left  end  of  the  valve  is  just  about  to  leave  the  square- 
blade  end.  The  eccentric  should  now  be  in  the  correct  position  for  perma- 
nent setting  for  the  selected  lead  of  ^2  in.  (15)  Fasten  the  eccentric 
securely  to  the  shaft  in  this  new  position;  the  valve  should  now  be 
set  properly. 

(16)  To  check  the  setting  for  accuracy,  turn  the  engine  to  the  head-end 
dead-center  position  and  also  measure,  as  described  in  14,  the  lead  at  this 


122    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

end.  If  the  valve  chest  is  not  the  same  at  both  ends,  it  will  be  necessary 
to  reset  the  combination  square  accordingly,  in  order  to  make  the 
measurement.  (17)  If  the  lead  at  both  ends  is  now  the  selected  lead  of 
^2  in.,  you  are  through.  If  it  is  not  ^2  in.  at  both  ends,  you  have  made 
some  error  and  if  so  repeat  the  necessary  preceding  steps  until  the  lead  at 
both  ends  is  K2  in.  —  or  is  the  selected  lead  whatever  it  may  be. 


Va/ve 


Steam  '•. 
Ports-'' 


- -L±  =  Lead,  Or  Lead  Equivalent,  With  Valve 
In  Extreme  Head-End  Position 


FIG.   168. — Determining  L\ — eccentric  of  a  plain  slide-valve  engine  in  extreme  head-end 
position.     (Exhaust  port  not  shown.) 

(18)  Replace  the  valve  chest  covers.  (19)  Check  your  setting  with  an 
indicator,  if  possible.  (20)  If  desirable,  spot  reference  marks,  as  else- 
where explained,  to  facilitate  future  rapid  setting  of  the  valve. 

EXAMPLE. — SETTING  THE  VALVE  OF  A  THROTTLING-GOVERNED,  PLAIN- 
D-SLIDE-VALVE  (DIRECT-VALVE)  ENGINE  FOR  SELECTED  EQUAL  LEADS. 
ECCENTRIC  Is  NOT  KEYED  To  SHAFT.  Follow  column  V  of  Table  167. 
Side  Graduations -^  A  24-inch  stroke  engine  is  to  be  set 

for  equal  selected  leads.  Proceed  as 
follows:  (1)  Select  the  amount  for 
the  equal  lead:  From  Sec.  165,  the 
proper  lead  for  an  engine  is  about  ^2 
in.  per  foot  of  stroke;  hence,  for  this 
engine  the  proper  lead,  which  will  be  designated  by  "Ls,"  is  Me  in.  (2) 
Establish  and  mark  the  dead-center  points  on  the  flywheel;  see  Sec.  153. 
(3)  Remove  valve-chest  cover.  (4)  Loosen  the  eccentric  and  rotate  it  on 
the  engine  shaft  to  its  extreme  head-end  position,  as  shown  in  Fig.  168. 


grl  i  I  i  I 


Mil 


hhl 


'-End  Graduations 

FIG.  169. — Steel  scale  having  end  grad- 
uations.     (Brown  &  Sharpe  Co.) 


-  End-Graduated  Steel  Scale 
-D-SI/de  Valve 
'  Valve 


&uide 
Block 


Eccentric 
Strap 


-Lead  Or  Lead  Equivalent 
With  Valve  In  Extreme 
Crank-End  Position 


Eccentric/ 

Rod''  Eccentric 


FIG.   170. — Determining  Lt — eccentric  of  a  plain  slide-valve  engine  in  extreme  crank- 
end  position.      (Exhaust  port  not  shown.) 


(5)  Measure  the  port  opening,  as  shown  in  Fig.  168  at  this  head  end; 
call  it  LI',  say  it  is  %  in.  A  steel  scale  which  has  end  divisions,  as  in  Fig. 
169,  is  convenient  for  making  such  measurements.  (6)  Rotate  the 
eccentric  on  the  engine  shaft  to  its  extreme  crank-end  position  as  shown 
in  Fig.  170.  (7)  Measure  the  port  opening,  L2,  at  this  crank  end.  If  this 


SEC.  167]        SLIDE  VALVES  AND  THEIR  SETTING 


123 


L2  happens  to  be  the  same  amount  as  Li,  the  port  openings  at  both  ends 
are  equal  which  shows  that  the  valve-stem  effective  length  is  correct. 
But  if  they  are  not  equal,  the  valve-stem  effective  length  will  have  to  be 
changed.  Assume  that,  in  this  example,  the  crank-end  port  opening; 
L2,  is  found  to  measure  *Me  in.  (8)  The  difference  between  Li  and  L2  = 
KG  -  H  =  %  -  %  =  Me  in. 

(9)  Then,  to  be  equal  at  each  end,  the  openings  must  be  changed  to 
L,  =  (Li  +  L,)  /2  =  (iMe  +  ^e)  -2  =  ^Me  -  2  =  %  in.  To 
make  the  openings  2>^2  in.  at  each  end,  the  valve-stem  effective  length 
must  be  changed  by  an  amount  equal  to  half  the  difference  between  LI 
and  L2  =  Me  -*-  2  =  H2  in.  Hence,  the  valve-stem  effective  length 
must  be  changed  by  ^2  in.  After  the  valve-stem  effective  length 
has  thus  been  changed  by  }$2  in.,  then  its  length  to  insures  that 
the  crank-end  and  head-end  steam  ports  will  always  have  equal  leads; 
this  regardless  of  the  amount  of  the  selected  lead,  the  setting  for  which  is 
made,  in  step  11,  by  changing  the  angle  of  advance  of  the  eccentric. 


FIG.  171. — Setting  a  plain  slide  valve  for  a  selected  lead,  L,. 
dead-center  position.) 


(Engine  is  in  crank-end 


(10)  Turn  the  engine  to  its  crank-end  dead-center  position.  (11) 
Change  the  angle  of  advance  so  that  the  equal  leads  at  both  crank  and 
head  ends  will  be  the  selected  lead,  L.  =  Me  m-  Proceed  thus:  Place 
the  eccentric  on  the  shaft  about  as  shown  in  Fig.  170  and  rotate  it  on  the 
shaft,  in  the  direction  that  the  engine  is  to  run  until  the  crank-end  port  is, 
see  Fig.  171,  open  just  the  KG  in.,  as  shown  by  measurement  with  an  end- 
divided  steel  scale.  (12)  Fasten  the  eccentric  securely  to  the  shaft  in 
this  new  position;  the  valve  should  now  be  set  properly. 

(13)  To  check  your  setting  for  accuracy,  turn  the  engine  to  its  head-end 
dead-center  position  and  also  measure  similarly  the  lead  now  shown  there. 
(14)  If  the  lead  at  both  ends  is  now  the  selected  lead  of  Me  in.,  you  are 
through.  If  it  is  not  Me  in.  at  both  ends,  you  have  made  some  error  and 
must  repeat  the  necessary  preceding  steps  until  the  lead  at  both  ends  is 
lie  in. — or  is  the  selected  lead  whatever  it  may  be.  (15)  Replace  the 
valve-chest  cover.  (16)  Check  the  valve-setting  with  an  indicator,  if 
possible.  (17)  If  desirable,  spot  reference  marks,  as  elsewhere  explained, 
to  facilitate  future  rapid  setting  of  the  valve. 

EXAMPLE. — SETTING  THE  VALVE  OF  A  SHAFT-GOVERNED,  PLAIN, 
INDIRECT- VALVE  (PISTON-VALVE)  ENGINE  FOR  DESIGN-DETERMINED 


124    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


EQUAL  LEADS.  (This  has  been  modified  from  an  article  in  Southern 
Engineer  for  November,  1919,  to  follow  the  procedure  which  is  specified 
in  Column  VIII  of  Table  167).  When  proper  reference  marks  have,  as 
hereinafter  described,  been  made  on  the  valve  stem  and  seat,  the  valve 
may  be  set  very  readily  and  quickly.  But  when  these  marks  do  not 
appear  and  no  templets  (Sec.  157)  are  available,  the  following  method 
may  be  pursued.  The  exhaust  port  is  not  shown  in  any  of  the  illustra- 
tions. The  numbers  in  parentheses  refer  to  the  step  numbers  in  Table 
167: 

(1)  Scribe  the  dead-center  marks  on  the  flywheel  as  explained  in  Sec. 
153.  (2)  Remove  the  valve-chest  covers.  (3)  Take  out  the  valve  and 

measure  the  length  (F,  Fig.  161)  of 
its  piston  portion;  say  it  is  2^  in. 
(4)  Adjust  a  combination  square  to 
the  length  shown  in  Fig.  162  with 
the  inner  end  of  its  blade  against 
the  inner  edge  of  the  steam  port; 
measure  this  distance,  M;  say  it  is 
4^  in.  If  the  chest  is  not  alike  at 
both  ends,  measure,  similarly,  the 
corresponding  distance  for  the 
other  end  of  the  chest.  (5)  Re- 
place the  valve  in  its  chest  and 
connect  it  in  running  order  to  the 
valve  stem.  (6)  Turn  the  engine 
in  its  running  direction  to  exact 
head-end  dead-center  position. 

(7)  Measure,  with  the  combination  square,  as  shown  in  Fig.  161,  the 
distance,  N,  to  the  valve  end;  say  it  is  l3^ 2  in.  Now  obviously  the  lead 
existing  on  this  end  is,  see  Fig.  172,  LI  =  M  -  (N  +  F)  =  4>^  — 
(13H2  +  2M)  =  4K  -  4Ke  =  H2  in.  (8)  Turn  the  engine  to  the 
crank-end  dead-center  position.  (9)  Similarly,  measure  the  lead,  L2, 
at  this  crank  end.  If  L2  happens  to  be  the  same  as  LI,  the  engine  is  set 
for  equal  design-determined  leads.  But  assume  that,  in  this  example, 
the  lead,  L2,  at  the  crank  end  is  found  to  be  ^2  in.  (10)  The  difference 
between  LI  and  L2  is  %2  —  ;Hj2  =  KG  in.  (11)  Then  the  proper  design- 
determined  equal  lead,  L3  =  (Li  +L2)/2  =  (}£2  +  ^2)  -*•  2  =  %  -*• 
2  =  KG  in. 

To  provide  this  KG  in.  equal  lead,  the  valve-stem  effective  length  must 
be  increased  by  an  amount  equal  to  half  the  difference  between  LI  and 
L2  =  (%2  —  ^2)  •*•  2  =  %2  -5-  2  =  M2  in.  Hence,  after  a  change  of 
^2  in.  in  the  valve-stem  effective  length,  the  engine  valve  should  be 
properly  set  for  design-determined  equal  leads.  Measure,  as  explained 
above,  the  new  lead  L3  to  be  sure  that  it  is  KG  in.  at  this  crank  end. 

(12)  Now,  for  a  check,  turn  the  engine  again  to  the  head-end  dead- 
center  position  and  by  measurement,  as  before,  check  the  new  lead  L3  for 
the  head  end.  (13)  If  the  leads  at  both  ends  are  equal,  you  are  through. 


FIG.  172.— Measuring  lead.     M  =  N  +  V 
+  Li  or,  Li  =  M  -  (N  +  V). 


SEC.  167]        SLIDE  VALVES  AND  THEIR  SETTING  125 

If  they  are  not  equal,  you  have  made  some  error  and  must  repeat  the 
necessary  preceding  operations  until  the  leads  are  equal.  (14)  Replace 
the  valve-chest  covers.  (15)  Check  your  setting  with  an  indicator  if 
possible.  (16)  If  desirable,  spot  reference  marks,  as  explained  below, 
to  facilitate  future  rapid  setting  of  the  valve. 

EXAMPLE. — THE  SPOTTING  OF  TRAM  REFERENCE  MARKS,  To  ENABLE 
ONE  To  QUICKLY  MAKE  FUTURE  VALVE  SETTINGS  WITHOUT  REMOVING 
THE  CHEST  COVERS,  is  effected  as  follows:.  It  is  assumed  that  the  valve 

pisfon         Valve-Chest  ,TmmmeI  Gage 


Valve 


Cover- . 


.  Eccentric - 

»  Direction 

^Combination  Of  Rotation --- 

Square  Rotation  Of  Crank 

Pin  OnCnank-End. 
Dead  Center 

FIG.  173. —  "Trying"  the  lead  at  the  crank  end  of  the  piston-valve  cylinder  (engine  on 
crank-end  dead  center). 

has  been  correctly  set  as  described  above.  Make  a  trammel  gage  (T7, 
Fig.  173)  by  pointing  the  two  ends  of  a  piece  of  steel  wire  and  bending  it 
into  trammel  form.  The  size  of  the  trammel — the  distance  between  the 
trammel  points — may  be  any  that  is  feasible  and  convenient.  With 
a  center  punch,  spot  a  mark  at  A  on  the  guide  block.  Place  one  point  of 
the  trammel  in  this  mark,  A,  and  then  spot  another  very  light  mark,  B, 
where  the  other  point  of  the  trammel  gage  touches  the  valve  stem.  These 
reference  marks  used  in  conjunction  with  the  trammel  gage  enable  one 
to  disconnect  the  valve  stem  from  the  stem  guide  block  and  to  then 

Steam  Stuffing  Position  Of  Crank 

Supply-  /  Box  Casting  Pin  On  Head-End 

'  Dead  Center- 


Eccentric 

Valve  Rod-' 

Stem  Direction  Of 

Rotation-...-? 

FIG.  174. — Locating  prick-punch  marks,  for  future  valve  settings,  on  valve  stem  and 
stuffing  box.     (Engine  on  head-end  dead  center.) 

replace  the  valve  (in  case  it  was  necessary  to  entirely  remove  the  valve) 
and  to  reconnect  the  valve  stem  in  exactly  its  original  position. 

Having  made  the  trammel  gage  and  used  it  as  in  Fig.  173,  now  again  use 
it  (Fig.  174)  for  spotting  the  slide-valve-lead  reference  marks.  Place 
the  engine  crank  on  exact  head-end  dead  center.  Then  spot  a  center 
punch  mark,  D,  (Fig.  174)  on  the  stuffing  box — not  on  the  gland.  Place 
one  end  of  the  trammel  gage  in  this  mark  and  spot  another  mark,  E,  on 
the  valve  stem  where  the  other  point  of  the  trammel  touches  the  stem. 


126     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

When  testing  to  verify  the  setting  of  the  valve:  First,  place  the  crank 
on  the  head-end  dead  center.  Then,  with  one  point  of  the  trammel  gage 
in  the  mark,  D,  the  other  gage  point  should  lie  exactly  in  the  punch  mark, 
E.  If  the  other  point  does  not  lie  in  E,  the  valve  setting  is  out  of  adjust- 
ment. With  the  gage  points  in  D  and  E,  assuming  that  the  original 
correct  adjustment  has  not  been  altered,  the  valve  will  have  opened  the 


Sheet-Stee/  Head-*. 


Smooth, Clear  Pine  Rocf 


k Long  Enough  To  Reach  Bottom 

Of  Steam  Chest  +6"  To  Spare 

FIG.   175. — Measuring  rod  for  measuring  steam-port  opening. 


head-end  port  to  the  amount  of  the  desired  lead — because  the  valve  was 
in  this  position  when  the  gage  and  the  marks  D  and  E  were  first  made. 
The  trammel  gage  should  be  carefully  preserved  so  that  in  future 
emergencies,  such  as  the  slipping  of  an  eccentric,  the  valve  can  be  promptly 
readjusted  to  its  correct  relation. 

EXAMPLE. — How  To  MAKE  THE  VALVE-SETTING  TEMPLETS  FOR  A 
PLAIN  INDIRECT- VALVE  (PISTON- VALVE)  ENGINE  will  be  explained: 
While  these  directions  relate  specifically  to  a  vertical  engine  they  may, 
with  obvious  modifications,  be  applied  to  a  horizontal  engine.  Compare 
this  method  with  the  similar  method  suggested  in  Sec.  157  and  that 
described  in  the  following  example  for  a  riding-cut-off  piston  valve;  all  of 

these  three  methods  vary  only  in 
detail  procedure,  the  final  result 
accomplished  in  each  being  essen- 
tially the  same.  Each  method  has 
its  applications. 

Make  A  Measuring  Rod,  as  shown 
in  Fig.  175,  for  locating  the  steam 
ports  in  the  valve  chest.  These 
steam-port  locations  will,  as  is  here- 


No.  1 6  Gage 
Sheet  5  fee/-. 


Index     I  N 

fi**--y" 

'Wooden 

(Preferably 

Stick 

FIG.   176. — Head  of  measuring  rod. 


inafter  described,  be  transferred  to 
the  steam-port  templet.  The  sheet- 
steel  head,  S,  (Fig.  176)  may  be  of 
approximately  the  proportions  there 
specified.  But,  in  any  case,  the 
in.  less  than  the  width  of  the  engine 


dimension  L  should  be  at  least 
steam  ports. 

Prepare  The  Sticks  From  Which  The  Templets  Will  Be  Made.  Two 
pieces  of  smoothed  clear  pine,  each  about  ^  in.  thick  and  about  1  in. 
wide  will  be  required.  Both  should,  at  the  start,  be  about  the  same 
length  as  the  measuring  rod.  All  faces  and  ends  should  be  square  and 
true. 


SEC.  167]        SLIDE  VALVES  AND  THEIR  SETTING 


127 


Prepare  To  Measure  The  Valve  Chest. — Remove  the  valve-chest  cover 
and  the  valve-stem  stuffing-box  gland.  Disconnect  and  remove  the 
valve  from  the  valve  chest. 

Make  The  Steam-Port  Templet. — Insert  the  measuring  rod  into  the  valve 
chest  so  that  one  of  its  index  edges  (Q,  Fig.  176)  is  against  the  furthest 
edge  of  the  farthest  steam  port  (Fig.  177,  7).  With  a  knife  blade,  cut  a 


t-Lower  Edge, 
Lower  Port 


I- Upper  Edge, 
Lower  Port 


Upper  ECW,,J, 
Upper  Port 


FIG.   177. — Marking  steam-port  locations  and  widths  of  a  vertical-engine  valve  chest  on  a 

measuring  rod. 

corresponding  line,  A,  on  the  face  of  the  rod  exactly  at  the  level  of  the 
valve-chest  face.  Similarly,  locate  on  the  measuring  rod  (as  shown  in 
Fig.  177,  77,  777,  and  IV)  lines  B,  C  and  D,  which  respectively  correspond 
to  the  other  edges  of  the  steam  ports.  Now,  as  shown  in  Fig.  178,  lay 
one  of  the  sticks,  which  was  prepared  as  above,  on  the  measuring  rod. 
With  a  try  square  and  knife  blade  transfer  the  lines  from  the  measuring 
rod  to  the  Y2  in.  face  of  the  stick.  In  the  illustrations,  the  width  of  the 


Steam-Port    .-Port  Locations^ 
Templet,      .'          /Center  Line .', 

W          /     •' C1      .'V        R' 

n    •      b-      VV^       £*•      V-^        •"_ 


;P/ston  Valve 


t--— Valve  Face 


« 


DC 

'Measuring 
Rod 


''Pencil  Hatch 
Lines  Drawn 
On  Templet 


::::  r 

:,  ^--Va/ve 

£ 

\ 

F  I 

'Valve  Temp/ef'- Center  Line 


~  •••/-•  - 

FIG.  178.— Laying  off  the  steam- port       FIG.  179.— Laying  off  the  valve  templet, 
templet. 

sticks  is  shown  exaggerated  for  clearness.  Draw  pencil  "hatch"  lines 
on  those  portions  of  the  stick's  face  which  do  not  represent  the  ports. 
Draw,  midway  between  C'  and  B'  a  knife-cut  center  line,  E,  across  the 
stick's  face.  This  completes  the  steam-port  templet. 

Make  The  Valve  Templet. — Lay  the  piston  valve  (Fig.  179)  on  the  1-in. 
face  of  the  other  stick  which  was  previously  made.     The  left  end  of  the 


128    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


valve  should  lie  about  H  in.  from  the  left  end  of  the  stick.  Transfer  to 
the  K-in.  face  of  the  stick  lines  representing  the  locations  of  the  edges 
of  the  valve  faces,  as  shown  in  Fig.  179.  Draw  a  center  line,  F,  midway 
between  the  two  sets  of  lines  which  represent  the  valve  edges.  Hatch, 
with  pencil  lines,  the  portions  of  the  stick's  face  which  represent  metal. 

The  Valve  Templet. Must  Be  Of  A  Certain  Length  so  that,  when  in  use 
(Fig.  180)  for  valve  setting,  it  will  reproduce  accurately  the  events  which 
are  occurring  in  the  steam  chest.  When  in  use,  the  lower  end  of  the  valve 
templet  rests  on  the  upper  end  of  the  valve,  while  the  valve  is  shifted 


Va/ve 
Temp/el •-,_ 

Lines  -. 

Representing, 
Va/ve  Edges  --'- 


Center  Lines / 
On  Temp/ets-',- 


Steam- 
Port  Templet 


^-Strap-Iron 
I   Support  (j 

''••Crank-End 
Steam  Port 


Valve    mPort 
Temple^  ^  Templet 


FIG.  180. — Templets   arranged  on  valve 
chest  for  valve  setting. 


,  Line 
C  Representing 
TV  Top  Face  Of 

•  Valve  Chest 


fHl 

JK-U 

-777/5  End  To 
•1.-T  Be  Cut  Off 

FIG.  181. — Measuring  valve  tem- 
plet to  cut  it  off  to  proper  length. 


vertically  to  different  positions.  The  valve  templet  slides  alongside  the 
steam-port  templet.  To  determine  the  proper  length  of  the  valve  tem- 
plet proceed  thus :  Lay  the  steam-port  templet  against  the  valve  templet 
(Fig.  181),  with  their  two  center  lines  F  and  E  exactly  in  line.  Now,  as  is 
evident  from  Figs.  177  IV  and  178,  the  distance  EH  on  the  steam-valve 
templet  equals  the  actual  distance  from  the  horizontal  center  line  between 
the  steam  ports  to  the  top  face  of  the  steam  chest.  Also,  the  distance  FI 
on  the  valve  templet  equals  (See  Figs.  179  and  181)  the  actual  distance 
between  the  horizontal  center  line  of  the  valve  and  either  end  face  of  the 
valve.  Hence,  from  Fig.  181,  it  follows  that  //  is  the  distance  which  the 
top  face  of  the  piston  valve  must  lie  below  the  top  face  of  the  valve  chest 
when  the  valve  is  vertically  central  in  the  valve  chest  in  relation  to  the 


SEC.  168]        SLIDE  VALVES  AND  THEIR  SETTING  129 

ports.  Now  lay  off  on  the  valve  templet  below  /  a  distance  JK,  which  is 
equal  to  IJ.  Cut  the  templet  off  square  at  K  and  it  will  be  complete  and 
of  correct  length. 

Arrange  The  Templets  On  The  Engine  Valve  Chest. — Bend  a  piece  of 
strap  iron  to  form  a  support,  G,  (Fig.  180)  for  the  steam-port  templet. 
Drill  the  short  leg  of  the  support  to  accommodate  one  of  the  valve-chest 
studs  and  drill  the  long  leg  to  take  three  round-head  wood  screws. 
Replace  and  reconnect  the  valve  in  the  chest.  Secure  the  steam-port 
templet  to  the  valve  chest  as  shown  in  Fig.  180,  with  the  "H"  end  of  the 
steam-port  templet  exactly  on  a  horizontal  line  with  the  top  face  of  the 
steam  chest.  Now  place  the  valve  templet  alongside  of  the  steam-port 
templet  (Fig.  180)  with  the  lower  end,  K,  of  the  valve  templet  resting  on 
the  upper  face  of  the  valve.  The  end  K  should  always,  when  the  tem- 
plets are  in  use,  rest  on  the  upper  end  of  the  valve.  Now,  if  the  templets 
have  been  accurately  made  they  will  visibly  reproduce,  outside  of  the 
steam  chest,  the  invisible  events  which  are  occurring  within  it. 

To  Use  The  Templets  For  Valve  Setting,  it  is  merely  necessary  to  follow 
the  directions  of  Table  167  and  measure  the  valve  events  which  occur 
from  the  templets — instead  of  measuring  them  directly  from  the  actual 
valve  and  ports.  After  the  valve  has  once  been  set  correctly,  it  may  be 
desirable  to  label  and  retain  the  templets  for  future  use.  But,  if  the 
proper  trammel  is  made  and  center-punch  reference  marks  are  spotted 
on  the  valve  stem  as  described  in  other  examples,  the  use  of  the  templet 
for  resetting  will  be  unnecessary. 

168.  Setting  A  Slide  Valve  For  Equal  Cut-Offs  has  definite 
limitations.  For  instance,  a  valve  designed  for  a  nominal 
cut-off  of,  say,  %o  stroke  could  not  give  satisfactory  operation 
if  set  for  £f  0  or  % o  cut-off  at  each  end.  In  setting  for  equal 
cut-offs,  one  must  not  attempt  to  depart  very  far  from  the 
nominal  cut-off  for  which  the  engine  was  designed.  The 
following  procedure  is  intended  to  give  a  practical  means  for 
setting  slide  valves  for  equal  cut-offs  which  will  give  satis- 
factory operation. 

(1)  Set  valve  for  proper  equal  leads  by  Table  167. 

(2)  Scribe  a  mark,  A,  (Fig.  182)  at  some  convenient  place  on  crosshead. 

(3)  Place  engine  on  crank-end  dead  center. 

(4)  Scribe  a   mark,  B,  on  the  crosshead  guide  opposite   A  on  the 
crosshead. 

(5)  Turn  engine  slowly  in  direction  it  is  to  run  until  the  valve  just  closes 
the  crank-end  cylinder  port  to  live  steam. 

(6)  Scribe  a  mark,  C,  on   the  crosshead  guide  opposite  A  on  the 
crosshead. 

(7)  Turn  engine  to  head-end  dead  center. 


130    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


(8)  Scribe  a  mark,  D,  on  the  crosshead  guide  opposite  A   on   the 
crosshead. 

(9)  Scribe  another  mark,  E,  making  DE  =  EC. 

(10)  Turn  engine  in  direction  it  is  to  run  until  A  stands  opposite  E  on 
the  guide. 

(11)  Change  effective  valve-stem  length  sufficiently  to  half  close  the 
cylinder  port. 

(12)  Move  eccentric  on  shaft  (opposite  to  engine  rotation)  to  just  close 
the  cylinder  port. 

(13)  Turn  engine  in  direction  it  is  to  run  until  cut-off  again  takes 
place  at  the  crank  end. 

(14)  If  A  is  not  opposite  C,  repeat  steps  (6)  to  (13). 

(15)  Check  valve  setting  with  an  indicator  (Sec.  175). 

NOTE.  —  SETTING  FOR  EQUAL  CUT-OFFS  Is  A  CUT-AND-TRY  ADJUST- 
MENT, it  being  necessary  usually  to  repeat  steps  (6)  to  (13)  several  times 
before  the  adjustments  are  correct. 


Crosshead 
on  Head -End 
Dead  Center, 


Connecting 


-Frame 


FIG.   182. — Method  of  marking  crosshead  guides  for  setting  valve  for  equal  cut-offs. 

169.  The  General  Procedure  In  Setting  A  Slide  Valve  For 
An  Intermediate  Between  Equal  Leads  And  Equal  Cut-Offs 
differs  from  that  for  equal  leads  (Sec.  167)  only  in  that  the 
adjustment  is  made  for  definite  unequal  leads.  The  lead  at 
the  head  end  is  made  a  little  less,  and  that  at  the  crank  end  a 
little  more,  than  the  value  recommended  in  Sec.  165.  The  dif- 
ference between  the  leads  at  the  two  ends  should  be  approxi- 
mately ^{Q  in.  for  each  foot  of  stroke.  The  result  of  this 
difference  is  to  eliminate  the  lead  at  the  head  end  (make  it 
zero)  and,  at  the  crank  end  to  double  the  value  given  in  Sec. 
165.  The  Ridgway  Engine  Co.  recommends,  for  engines  of 
14  in.  stroke  and  smaller  that  the  lead  should  measure  ^2  m- 
more  at  the  crank  than  at  the  head  end  and  for  larger  engines 
J/16  in.  more  at  the  crank  than  at  the  head  end.  The  pro- 
cedure therefore  becomes: 


SEC.  170]        SLIDE  VALVES  AND  THEIR  SETTING  131 

(1)  Establish  dead  centers  (Sec.  153). 

(2)  Remove  valve-chest  cover. 

(3)  If  engine  has  shaft  governor,  it  may  be  necessary  to  block  the  gov- 
ernor to  its  normal  operating  position  (See  Sec.  174). 

(4)  With  indirect  valve,  remove  the  valve  and  measure  it.     If  necessary 
make  templet   (Sec.   157). 

(5)  With  indirect  valve,  measure  valve  seat  and,  if  necessary   make 
templet  (Sec   157). 

(6)  Replace  valve  on  seat. 

(7)  Set  engine  on  head-end  dead  center. 

(8)  Rotate  eccentric  on  shaft,  in  direction  engine  is  to  run,  until  the 
lead  at  head  end  is,  say,  M  in. 

(9)  Measure  accurately  the  lead  at  this  end.     Call  it  L\. 

(10)  Fasten  eccentric  to  shaft. 

(11)  Turn  engine  to  crank-end  dead  center. 

(12)  Measure  lead  at  crank  end.     Call  it  L2. 

(13)  Change  lead  at  this  end  so  that  L2  —  LI  =  K  =  the  proper  differ- 
ence between  the  leads  at  the  two  ends.     Make  the  adjustment  by  chang- 
ing the  valve-stem  length. 

(14)  Shift  eccentric  to  attain  the  required  lead  at  this  (crank)  end. 

(15)  Replace  valve-chest  cover. 

(16)  Check  setting  with  indicator  (Sec.  175). 

NOTE. — WHEN  VALVES  ARE  THUS  SET  FOR  UNEQUAL  LEADS  THE 
RESULTING  INDICATOR  DIAGRAMS  WILL  SHOW  admission  occurring  too 
early  at  the  crank  end  and  too  late  at  the  head  end.  This  must  be 
tolerated  because  it  is  a  consequence  of  the  valve  setting.  Should  the 
engine,  however,  appear  to  "pound"  at  the  crank  end,  the  eccentric 
must  be  turned  backward  on  the  shaft  or  the  valve-stem  length  must  be 
changed  until  the  pounding  stops. 


170.  Multiported  Valves  Are  Set  by  following  the  same 
general  rules  as  outlined  from  Sec. 
167  to  Sec.  169.  Multiported 
valves  are  generally  so  designed 
that  cut-off  and  the  other  events 
occur  at  each  valve  port  at  the 
same  time.  For  example,  Fig. 
183  shows  that  head-end  admis-  lB^SJ^^^/J^rT ^TT 

•11  ji  <•  Port  'c.E. Cylinder 

sion  will  occur  at  the  same  time  Port 

past    edges  A    and    B.       Obviously     FIG.   IBS.— A  multiported  slide  valve 
rf  ,i  i  at  the  point  of  head-end  admission. 

cut-off  must  occur  at  these  edges 

at  the  same  time.     Therefore  the  setting  of  valves  of  this 

type  requires  no  special  explanation.     Each  particular  valve 


132    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

should  be  examined  for  peculiarities.     Templets  may  be  made 
of  the  valve  and  the  seat  to  facilitate  future  setting. 

171.  A  Method  Of  Setting  Any  Slide  Valve  Without  Remov- 
ing The  Steam-Chest  Cover  (Power,  Nov.  15,  1921)  is 
described  below.  This  applies  to  plain  D,  piston,  balanced, 
and  multiported  slide  valves — in  fact  to  any  slide  valve. 
However  the  method  can  be  used  effectively  only  for  engines 
which  have  little  or  no  valve  leakage;  this  restricts  it,  largely, 
to  relatively-new  or  to  recently-overhauled  engines. 

EXPLANATION. — //  there  is  a  rocker  for  transmitting  motion  of  the 
eccentric  to  the  valve  rod,  for  the  best  valve  setting  the  length  of  the 
eccentric  rod  should  be  so  adjusted  that  the  rocker  will  swing  approxi- 
mately as  far  to  one  side  as  to  the  other  of  that  position  in  which  it  would 
be  at  right  angles  to  the  valve  rod.  After  the  length  of  the  eccentric  rod 
has  been  thus  adjusted,  the  valve  setting  is  completed  by  adjusting  the 
valve  rod  to  such  length  that  one  end  of  the  valve  will  travel  over  the 
opening  edge  of  its  steam  port  as  much  as  the  other  end  of  the  valve  will 
travel  over  the  opening  edge  of  its  port  and  then  with  the  engine  on  a 
center,  setting  the  eccentric  to  that  position  which  will  give  the  valve 
the  desired  amount  of  lead.  How  this  may  be  done  is  explained  below. 

//  the  valve-rod  length  cannot  be  adjusted  outside  of  the  stuffing  box,  it  will 
be  necessary  for  good  valve  setting  to  remove  the  steam-chest  cover 
for  that  purpose.  But  where  the  rocker  would  be  thrown  only  slightly 
out  of  perpendicular  to  the  valve  rod  by  adjusting  the  length  of  the  eccen- 
tric rod,  then  a  fair  valve  setting  can  be  effected  by  simply  adjusting  the 
length  of  the  eccentric  rod  for  equalizing  the  travel  of  the  valve  without 
opening  the  steam  chest.  Or  in  case  there  is  no  rocker,  the  equalization 
of  valve  travel  can  be  effected  by  adjusting  either  the  length  of  the  valve 
rod  or  the  length  of  the  eccentric  rod,  without  removing  the  steam-chest 
cover. 

For  testing  the  equalization  of  valve  travel  without  opening  the  steam 
chest:  Place  the  engine  on  a  center,  make  a  mark  on  the  guide  to  corre- 
spond with  a  mark  on  the  crosshead.  Temporarily  fasten  the  eccentric 
on  the  shaft  in  that  position  which  will  just  permit  steam  to  be  blown 
through  the  port  at  the  same  end.  Then,  turn  the  flywheel  forward  to 
the  position  where,  by  opening  the  throttle  valve,  very  little  steam  is 
shown  by  the  pet  cock  to  be  admitted  to  the  other  end  of  the  cylinder. 
Make  a  mark  on  the  guide  to  correspond  with  the  mark  on  the  crosshead. 
Also  make  another  mark  with  the  engine  on  dead  center  at  the  same  end 
of  the  cylinder.  Also  make  a  mark  on  the  guide  halfway  between  the 
marks  last  made  on  the  guide.  Then  turn  the  engine  wheel  to  such  a 
position  that  the  mark  on  the  crosshead  will  be  opposite  to  this  middle 
mark.  Adjust  the  length  of  the  valve  rod  or  eccentric  rod  so  steam  will 
be  just  admitted  on  the  same  end. 


SEC.  172]        SLIDE  VALVES  AND  THEIR  SETTING  133 

Next  turn  the  engine  forward  toward  the  other  center  until  the  mark  on 
the  crosshead  comes  the  same  distance  from  the  end  of  the  stroke  as  the 
middle  mark  is  from  the  other  end.  If  steam  is  just  admitted  the  travel 
has  been  equalized.  If  not,  turn  the  engine  to  the  position  where  steam 
is  just  admitted.  Make  another  mark  on  the  guide  halfway  between 
the  position  where  steam  was  admitted  and  the  position  where  it  should 
have  been  admitted.  With  the  crosshead  set  at  this  middle  mark, 
readjust  the  valve-rod  or  eccentric-rod  length  until  steam  is  admitted  at 
that  end  of  the  cylinder. 

Now  set  the  valve  for  the  desired  amount  of  lead.  With  the  valve  travel 
thus  equalized,  place  the  engine  on  the  head-end  center.  Turn  the  eccen- 
tric forward  on  the  shaft,  and  set  the  eccentric  to  the  position  at  which 
steam  is  just  admitted  to  the  head  end  of  the  cylinder.  Then  make  a 
mark  on  the  valve  rod  exactly  1  in.  out  from  the  end  of  the  stuffing-box 
gland.  Shift  the  eccentric  as  much  farther  forward  on  the  shaft  as  may 
be  necessary  to  shift  the  mark  made  on  the  valve  rod  by  a  distance  equal 
to  the  desired  amount  of  lead. 

172.  Setting  A  Riding  Cut-Off  Valve  Mechanism  must, 
since  it  contains  two  valves,  be  accomplished  in  two  steps, 

(1)  THE  MAIN  VALVE  Is  SET  for  equal  leads  by  the  method  of  Table 
167  or  as  follows :  Rotate  the  eccentric  from  one  extreme  position  to  the 
other  to  see  that  both  cylinder  ports  are  opened  to  the  same  extent. 

If  they  are  not,  adjust  (Table  167)  the  valve-stem  effective  length 
until  they  are.  Whether  they  open  exactly  to  their  total  width  is  not 
important.  Then  put  the  engine  crank  on  the  head-end  dead  center  and 
have  the  eccentric  rotated,  in  the  direction  in  which  the  engine  is  to  run, 
until  the  head-end  cylinder  port  begins  opening  and  is  open  by  the  amoun  t 
of  the  lead  (usually  ^2  in.).  This  may  often  be  determined  by  observing 
the  cylinder  port  through  the  port  in  the  main  valve.  Then  fasten 
the  eccentric  securely  to  the  shaft.  The  valves  of  a  piston-valve  engine 
must  be  set  by  an  indirect  method,  such  as  that  which  is  described  in  the 
following  example. 

(2)  SETTING  THE  CUT-OFF  VALVE  is  dependent  upon  whether  the  cut- 
off valve  is  (a)  hand-adjustable,  (6)  governor-operated,  (c)  neither  hand- 
adjustable  nor  governor-operated.     In  any  one  of  these  three  constructions 
the  first  step  is  to  adjust  the  valve-stem  length.     To  do  this,  place  the 
main  valve  in  its  mid-travel  position  and  turn  the  cut-off  eccentric.     The 
cut-off  valve  should  travel  equal  distances  beyond  the   two  ports  of 
the  main  valve.     If  it  does  not  do  this,  adjust  the  effective  valve-stem 
length  until  it  does. 

(a)  //  the  cut-off  valve  is  hand-adjustable:  Make  marks  A  and  D  (Fig. 
182)  on  the  crosshead  and  guide  to  represent  the  head  end  of  the  stroke. 
With  the  engine  still  on  head-end  dead  center,  place  the  cut-off  eccentric 
on  its  crank-end  center  (Sec.  154)  and  fasten  it  there  by  tightening  its 
set  screws.  Now  measure  two-thirds  stroke,  DE,  from  the  head-end 


134     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


mark  D  on  the  crosshead  guide  and  make  another  mark,  E,  on  the  guide. 
Turn  the  engine  in  the  direction  it  is  to  run  to  bring  the  crosshead  mark  A 
to  this  last-made  mark,  E,  on  the  guide.  Then  adjust  the  position  of  the 
cut-off  valve  on  its  stem  (by  the  hand  wheel,  Fig.  184)  until  it  just  closes 
the  head-end  port  of  the  main  valve.  This  completes  the  setting. 

(6)  //  the  cut-off  valve  is  governor-operated:  With  the  governor  connected 
up  and  its  weights  resting  at  their  inner  positions,  turn  the  flywheel  until 
cut-off  occurs  and  measure  the  fraction  of  stroke  at  which  this  occurs. 
Do  this  for  the  forward  and  return  strokes.  The  fractions  should  be 
equal  if  the  valve  stems  are  of  proper  length.  If  the  fractions  are  unequal 
they  may  be  equalized  by  changing  the  effective  length  of  the  cut-off 
valve  stem.  Then,  the  governor  springs  should  be  disconnected  and 
the  weights  blocked  out  against  their  stops.  Turning  the  flywheel  now 
should  not  cause  the  cut-off  valve  to  uncover  the  ports  of  the  main  valve 
at  any  position  during  the  revolution. 


^-Adjusting  Handwhee/ 

Riding  Cut-Off 


.Left-Hand 
Thread 


Fio.  184. — Section  of  a  Meyer  riding-cut-off  valve. 

(c)  //  the  cut-off  valve  is  neither  hand-adjustable  nor  governor-operated: 
Place  the  engine  on  head-end  dead  center  and  the  cut-off  eccentric  on  its 
crank-end  center  and  fasten  it  there,  just  as  in  (a).  Now  turn  the  engine 
ahead  for  %  stroke  (or  whatever  fraction  of  stroke  at  which  cut-off  is 
desired)  of  the  crosshead,  as  in  (a).  Now  loosen  the  cut-off  eccentric  and 
shift  it  ahead  (in  the  direction  the  crank  is  to  turn)  until  it  closes  the 
head-end  port  in  the  main  valve.  Then  fasten  the  eccentric  securely. 
The  setting  is  thus  completed. 

The  following  example  illustrates  the  application  of  the  preceding  rules 
to  the  setting  of  a  riding-cut-off  piston-valve  engine's  valves. 

EXAMPLE. — SETTING  THE  VALVES  OF  A  SHAFT-GOVERNED  PISTON- 
RIDING-CUT-OFF-VALVE  ENGINE  for  selected  equal  leads.  This  is  based 
on  the  directions  in  an  article  in  Southern  Engineer  for  December,  1919. 
An  indirect  method  (Sec.  156)  must  be  employed.  While  the  detail 
procedure  herein  outlined  is  riot  exactly  the  same  as  that  specified  in  the 
general  directions  of  Sec.  172  above,  the  result  which  is  attained  is  the 
same. 


SEC.  172]        SLIDE  VALVES  AND  THEIR  SETTING 


135 


These  directions  relate  specifically  to  an  engine  of  " Buckeye"  con- 
struction, the  valve  and  cylinder  arrangement  of  which  is  shown  in  Fig. 
185.  There  are  two  piston  valves,  Vi  and  V2  (Fig.  185)  one  working 
within  the  other.  The  working  edges  of  neither  are  visible  when  one 
is  setting  the  valves.  The  cylindrical  end  portions,  E,  of  the  main 
valve,  Fi,  form  two  smaller  valve  chests  for  the  cut-off  valve.  The  two 
cup-like  ends  of  the  main  valve  are  retained  in  correct  relation  by  three 
rods,  R,  which  tie  the  ends  together.  The  hollow  main-valve  stem, 
M,  is  screwed  into  that  main-valve  head  which  lies  nearest  the  crank. 
The  cut-off-valve  stem,  C,  slides  longitudinally  within  the  main- 
valve  stem. 


Stationary  Valve-    ..Main 
Chesf  Liner         .•'    Valve 


Riding  Cut- 
Off  Valve. 


-Cylinder  Head 


FIG.   185. — Piston-type  riding-cut-off  valve.      (Longitudinal  section  through   cylinder 
and  valve  chest  of  "Buckeye"  simple  engine.) 


Prepare  To  Set  The  Valve. — Remove  the  valve-chest  cover.  Disconnect 
the  valve  rods  from  the  rocker  shafts.  Remove  the  valves  and  place 
them  on  a  bench.  Now,  since  the  valve  ports  are  invisible  when  the 
valves  are  in  the  valve  chest,  templets  (Sec.  157)  must  be  made  whereby 
the  invisible  events  which  occur  inside  the  valve  chest  will  be  reproduced 
outside  of  it,  where  the  events,  thus  reproduced,  will  be  visible. 

Make  The  Steam-Port  Templet. — First,  make  a  wooden  measuring  rod 
(R,  Fig.  186);  it  should  be  of  smoothed  clear  pine,  about  1  in.  wide 
%  in.  thick  and  somewhat  longer  than  the  steam  chest.  Cut  one  end  to 
the  shape  which  is  shown  at  the  right  in  Fig.  186.  To  take  the  measure- 
ments for  the  steam-port  templet,  place  the  shaped  end  of  the  rod  against 
the  inner  steam-port  edge  as  shown.  Then,  with  a  knife  blade,  mark  the 
width  of  the  outer  port  with  two  fine  lines,  X  and  Y  (Fig.  186).  Remove 
the  rod  from  the  chest  and  mark  the  width  of  the  other  steam  port  on  the 
rod :  Measure  the  width  between  X  and  Y  and  lay  off  this  width  from  the 
shaped  end  of  the  rod,  as  shown  at  Z  in  Fig.  187.  Cut  a  smoothed  clear 


136     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


pine  branch  board,  S,  (Fig.  187)  for  a  steam-port  templet.  It'^may  be 
%  in.  thick,  4  in.  wide  and  about  the  length  of  the  valve-chest.  Lay  the 
rod  on  the  board  and  transfer  the  locations  of  the  ports  from  the  rod  to  the 
board,  as  shown  in  Fig.  187.  Draw  pencil  "hatch"  lines  along  the  length 
of  the  board  which  does  not  represent  the  steam  ports. 


Stationary  Liner 
{    Or  Bushing 


'Wooden     "-Head- End          ''--.. 

Measuring      Steam  Port 

Rod  Crank- End  Steam  Port' 

FIG.  186. — Using  measuring  rod  for 
determining  steam-port  locations  and 
widths. 


Wooden 
•'Measuring  Rod 


,  z 


•Is 


„ 


'Pencil  Hatch  "  ~  -Marks  Indicating 
Lines  Drawn       Port  Locations  \ 

On  Templet         And  Widths,  lf  } 

Steam-Port  Templet  (Q  Wooden- 
Piece) 

FIG.  187.  —  Transferring  steam-port 
locations  and  widths  to  the  steam-port 
templet. 


Make  The  Main-Valve  Templet— Cut  apiece,  M(Fig.  188),  of  smoothed 
clear  pine  %  in.  by  2  in.  and  somewhat  longer  than  the  main  valve. 
Hold  M  edgewise  against  the  main  valve  and  mark,  with  knife  cuts,  the 
locations  of  the  valve  ports  and  the  valve  ends,  as  shown  in  Fig.  188. 
Now,  if  the  main-valve  templet  is  placed  on  the  steam-port  templet, 
(Fig.  189)  the  exact  relative  positions  of  the  two  sets  of  ports  will  be 
shown.  The  portions  of  M  which  represent  metal  should  be  pencil 
hatched  as  suggested  in  Fig.  189. 


•Riding  Cui-Off-Valve    Cut-Off-  Valve  Rod* 
,.- Main  Valve      Main-Va/ve  Rod*      \ 


'Port  -Main-Valve 

LocationMarks    .     Templet 
^Valve-Length  Location  Marks 

FIG.  188. — Transferring  the  length  of 
the  main  valve  and  the  valve-port  widths 
and  locations  to  the  main-valve  templet. 


•.Marks  Indicating  Ends  Of  Main  Valve*. 
;  Main-Valve  Port  Locations*,       \ 


'Hatch  L  ines      '  •  {5team-Port        ''Steam- 
Drawn  On  Board     Marks  Port 
In  Pencil                                      Templet 

FIG.  189. — Main- valve  templet  and 
steam-port  templet  in  correct  mid- 
travel  positions  showing  the  relations 
between  the  ports  in  each. 


Spot  Cut-Off-Valve-Position  Marks  On  The  Cut-Off-Valve  Rod  thus: 
Slide  the  cut-off  valve  inside  of  the  main  valve  until  the  left  end  of  the 
cut-off  valve  just  closes  the  port,  P  (Fig.  190).  Make  a  trammel  gage,  T. 
of  steel  wire.  Spot  a  center-punch  mark,  C,  on  the  main-valve  stem. 
Place  one  point  of  T  in  C  and  under  the  opposite  point  of  T  spot  another 
center-punch  mark,  C",  on  the  cut-off-valve  stem.  Now,  slide  the  cut-off 
valve  to  the  right  within  the  main  valve  until  the  right  end  of  the  cut-off 


SEC.  172]        SLIDE  VALVES  AND  THEIR  SETTING 


137 


valve  just  closes  the  other  main-valve  port,  Q.  With  the  punch  and  gage 
spot  the  corresponding  mark,  D,  on  the  cut-off  valve  stem.  Obviously, 
when  one  end  of  the  gage,  T,  is  in  C  and  the  cut-off  valve  is  shifted  until 
the  other  gage  end  lies  in  either  D  or  C",  the  corresponding  port  in  the 
main  valve  will  have  just  been  closed. 

Arrange  The  Templets  In  Position  For  Setting  The  Valve. — Replace  both 
valves  in  the  valve  chest.  Arrange  two  saw  horses  or  a  bench  to  support 
the  steam-port  templet  (Fig.  191)  in  line  with  and  at  the  same  elevation 
as  the  bottom  of  the  valve  chest.  Place  the  main-valve  templet  edge- 


.-Ri'ding-Cut-Off  Valve 
Valve 


Trammel 

Cut-Off         Gage- 
Val 


FIG.   190. — Center-punch  marks  and  gage  for  adjusting  the  cut-off-valve  stem  and  the 

cut-off  valve. 

wise  (Fig.  191)  on  the  steam-port  templet.  Provide  a  metal  strap,  H, 
and  so  fasten  it  with  screws  to  the  main-valve  templet  that  the  projecting 
end  of  the  strap  just  touches  the  left  end  of  the  main  valve,  when  all  are 
in  the  positions  shown  in  Fig.  191 :  That  is,  have  the  main-valve  eccentric, 
turned  to  such  a  position  that  the  left  end  of  the  main  valve  is  in  line  with 
the  head-end  steam  port  edge  as  shown  at  Q  in  Fig.  191.  Now  shift 
longitudinally  the  steam-port  templet  until  marks  M  and  N  are  in  line. 
Secure  the  steam-port  templet  in  this  position  to  the  bench  or  horses,  with 
nails  driven  part  way  in.  The  two  templets  should  now  accurately 
represent  the  relative  positions  of  the  main  valve  and  the  steam  ports 


Main  -  Valve  Metal 

Templet-- .  Strip 


Valve  Chest- 


N'       G''     Steam-Port  1* 

Templet'"'      Main  Valve'' 

FIG.  191. — Templets  arranged  at  end  of  valve  chest  ready  for  setting  the  valves. 

When  the  main  valve — and  the  main-valve  templet  with  it — is  moved 
back  and  forth  in  its  seat  the  results  are  reproduced  by  the  templets. 

Adjust  The  Effective  Lengths  Of  The  Eccentric  Rods  So  That  The  Valves, 
When  At  The  Ends  Of  Their  Travels,  Will  Open  The  Head-End  And  The 
Crank-End  Ports  By  Equal  Amounts. — Since  the  cut-off  valve  should  be 
adjusted  with  reference  to  the  main  valve,  the  main  valve  should  be 
adjusted  first. 

Adjust  The  Main-Valve  Eccentric  Rod  To  Correct  Effective  Length. — 
Turn  the  main  eccentric  to  one  dead-center  position  (Fig.  165)  and 


138    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

measure  from  the  templets  (Fig.  191)  the  distance  that  the  edge  of  the 
corresponding  valve  has  over-ridden  the  edge  of  its  steam  port,  or,  instead, 
the  distance  that  the  valve  should  move  to  entirely  open  the  port.  Then, 
turn  the  eccentric  to  the  opposite  dead-center  position  (Fig.  163)  and 
note  the  relative  location  of  the  valve  edge  and  port  edge  in  this  position. 
If,  in  both  positions,  the  valve  either  opens  the  ports  by  the  same  amount 
or  over-rides  the  ports  by  the  same  amount,  the  head-end  and  crank-end 
travels  are  equal  and  the  main-eccentric-rod  effective  length  is  correct. 
If  this  eccentric-rod  effective  length  is  not  correct,  it  may  be  adjusted  to 
correct  length  as  directed  in  Table  167. 

Adjust  The  Cut-Off-Valve  Eccentric  Rod  To  Correct  Effective  Length; 
proceed  thus:  Place  the  main  valve  in  its  mid- travel  position  (Fig.  189)  as 
indicated  by  the  templets.  Secure  it  in  this  position  by  clamping  the 
main-rod  stuffing-box  gland.  Rotate  the  governor  wheel  until  the  cut-off 
eccentric  is  on  its  head-end  (Fig.  163)  dead  center.  Then  with  one  point 
of  the  gage,  T  (Fig.  190),  in  center-punch  mark,  C,  measure  the  distance 
of  the  other  gage  point  from  the  punch  mark,  C",  on  the  cut-off  valve  stem. 
Now,  retain  one  point  of  the  gage  in  C  and  have  the  cut-off  eccentric 
turned  to  the  crank-end  dead-center  (Fig.  165)  position.  Note  the  dis- 
tance the  gage  point  is  from  D.  If  these  two  distances  are  equal,  the 
cut-off-eccentric-rod  effective  length  is  correct.  If  it  is  not  of  correct 
length,  adjust  it  to  correct  length  as  directed  in  Table  167. 

Set  The  Main-Valve  Eccentric  For  Selected  Equal  Leads. — Loosen  the 
stuffing-box  gland  which  clamped  the  main-valve  stem.  Turn  the  engine 
crank  to  its  head-end  dead-center  position  and  rotate  the  main-valve 
eccentric  to  its  head-end  center  position,  Fig.  163.  [When  a  direct  valve 
gear  (one  which  does  not  employ  levers  which  change  the  direction  of  the 
valve-stem  movement  from  that  of  the  eccentric-rod  movement)  and  a 
piston  valve  is  employed,  the  valve  on  opening  its  port  for  the  admission 
of  steam  moves  in  a  direction  opposite  to  the  direction  of  motion  of  the 
piston.  The  main-valve  gear  of  the  Buckeye  engine  is  "direct."] 
Therefore  if  the  crank  is  to  run  "over"  the  eccentric  should  be  turned 
in  the  opposite  direction,  or  under,  until  the  port  at  the  head  end  of  the 
cylinder  remains  open  only  by  the  extent  of  the  selected  lead.  The 
proper  lead  may  be  determined  as  explained  under  "Selected  Lead"  in 
Sec.  165;  it  should  on  engines  of  this  type  seldom  exceed  Me  in.  This 
lead,  in  any  case,  is  measured  as  the  distance  between  the  lines  F  and  G  in 
Figs.  189  and  191  on  the  templets.  After  it  has  been  thus  set  for  the 
selected  lead,  secure  the  main  eccentric  to  the  shaft.  The  main  valve 
should  now  be  properly  set.  To  check  the  lead  at  the  opposite  end  to 
insure  accuracy,  turn  the  engine  crank  to  the  opposite  dead  center  and 
measure  the  lead  which  shows  with  this  position.  If  the  lead  is  not  the 
amount  selected  and  is  not  the  same  at  both  ends,  it  will  be  necessary  to 
change  the  eccentric  rod  effective  length  and  the  angle  of  advance  as 
directed  in  Table  167,  until  the  lead  is  the  amount  selected  and  is  the  same 
at  both  ends. 


SEC.  172]        SLIDE  VALVES  AND  THEIR  SETTING 


139 


Set  The  Cut-Off  Valve  Eccentric. — -Turn  the  engine  shaft,  starting  at  the 
head-end  dead  center,  in  the  engine's  running  direction  until  the  main 
valve,  the  eccentric  of  which  is  now  properly  secured  to  the  engine  shaft, 
just  closes  the  port  in  the  valve  seat.  This  is  the  cut-off  point  for  the 
main  valve.  Loosen  the  governor  wheel  from  the  engine  shaft.  Now, 
starting  with  the  cut-off  eccentric — or  the  governor  wheel — at  the  eccen- 
tric's head-end  dead  center  position,  turn  it  in  the  engine's  running 
direction,  until  the  cut-off  valve  just  closes  the  port  in  the  main  valve. 
This  position  is  determined  by  placing  one  point  of  T  (Fig.  190)  in  C 
and  shifting  the  cut-off  eccentric  until  the  mark,  C',  lies  under  the  other 
gage-point  as  shown  in  Fig.  190.  The  full  part  of  the  cut-off  eccentric 
should  now  project  from  the  shaft  on  the  same  side  and  in  approximately 
the  same  direction  as  does  the  crank  itself.  Secure  the  cut-off  eccentric 


'^Engine  Cylinder 

Trammel 


Cut-Off-Valve 
Center-Punch 


3 


'Main-Va/ve 

,-•''  Center- Punch 

'Main-  Marks 

Valve  Rod 


FIG.  192. — Punch  marks  to  insure  future  rapid  setting  of  the  main  valve. 

(governor  wheel),  as  thus  set,  to  the  engine  shaft.     Both  main  and  cut-off 
valves  should  now  be  properly  set. 

Spot  Identifying  Marks  On  the  Main-Valve  Stem  To  Facilitate  Its  Future 
Rapid  Setting. — Make  another  trammel  gage,  as  T2  in  Fig.  192.  Place 
the  engine  crank  on  dead  center  again.  Spot  a  center-punch  mark,  V, 
on  the  steam-chest  head.  Place  the  straight  point  of  Tz  in  V  and  spot  a 
center-punch  mark,  E,  on  the  main  valve  stem  under  the  other  point  of 
Tz.  Turn  the  crank  to  the  opposite  dead-center  position  and  spot 
another  center  punch  mark,  under  the  extending  gage  point,  at  H.  It  is 
evident  that,  when,  at  any  future  time,  the  main-valve  stem  is  brought 
into  the  position  shown  in  Fig.  192  and  as  determined  with  T2,  the  main 
valve  will  have  just  opened  the  port  to  the  extent  of  the  selected  lead. 
Hence,  by  employing  T2  and  the  marks  H  and  E,  the  main  valve  may  be 
readjusted  without  removing  it — or  even  the  valve-chest  cover.  Bisect 
the  distance  between  H  and  E  and  spot  another  punch  mark  at  the  point 
of  bisection,  7.  Now,  if,  in  the  future,  7  is  brought  under  the  extending 


140    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

gage-point,  then  the  main  valve  will  occupy  its  mid- travel  position;  this 
position  must  be  determined  in  adjusting  the  cut-off-valve  eccentric  rod 
effective  length,  as  before  directed.  Replace  the  valve-chest  cover  and 
move  the  engine  crank  from  "dead  center"  and  the  job  is  finished. 

Preserve  The  Trammel  Gages. — Drill  a  small  hole  through  each  gage. 
Tag  them  respectively  "main  valve"  and  "cut-off  valve."  Tie  them 
together  and  lay  them  away  in  a  safe  place.  The  wooden  templets, 
which  were  employed  in  setting  the  valves,  need  never  again  be  used. 

173.  To  Reverse  The  Direction  Of  Rotation  Of  A  Slide- 
Valve  Engine :  For  a  throttling  governed  engine,  place  the  engine 
in   the   head-end  dead-center  position.     The  lead  or  lag  of 
the  eccentric  will  then  indicate  the  direction  of  rotation:  With 
outside-admission  valves  (Sec.  136)  the  crank  pin  always,  if  there 
is  no  eccentric-rod  reversing  rocker,  follows  the  eccentric.     With 
inside-admission  valves  (Sec.  136)  the  eccentric  always  follows 
the  crank.    Loosen  the  eccentric  and  turn  it  about  the  shaft 
so  that  it  leads,  on  lags  behind,  the  crank  pin  for  the  new 
direction  of  rotation  by  the  same  angle  as  it  lagged  behind, 
or  led,  the  crank  pin  for  the  old  direction  of  rotation.     The 
lead  of  the  valve  will  be  the  same  as  before.     In  fact,  an  often 
convenient  method  of  reversing  the  direction  of  rotation  is, 
the  engine  being  on  dead  center,  to  measure  the  observed 
lead  and  then  shift  the  eccentric  around  the  shaft,  which  will 
pull  over  the  valve,  until  exactly  the  same  lead  is  shown  at  the 
same-end  steam  port.     Then  secure  the  eccentric  in  its  new 
position  and  the  job  is  completed. 

NOTE. — IP  A  REVERSING  ROCKER  Is  USED  IN  THE  ECCENTRIC  GEAR, 
the  eccentric  must  be  placed  on  the  shaft  exactly  on  the  opposite  side 
from  that  which  it  would  occupy  if  no  reversing  rocker  were  employed. 
That  is,  with  outside-admission  valves,  the  eccentric  will  follow  the  crank; 
with  inside-admission  valves,  the  crank  will  follow  the  eccentric.  With 
this  in  mind,  the  above  rules  may  be  followed  for  reversing  the  rotational 
direction  of  engines  with  reversing  rockers. 

174.  How  Governors  Affect  Slide-Valve  Setting.  (1)  Throt- 
tling governors  have  no  bearing  on  the  valve  motion  and,  there- 
fore, need  no  special  attention.     Valves  on  engines  having 
throttling  governors  have  the  same  motion,  irrespective  of 
the  engine  load.     (2)  Variable-cut-off  governors,  shaft  governors 
for  example,  change  the  motion  of  the  valves  with  changes  in 
engine-load  and,  therefore,  require  consideration  when  adjust- 


SEC.  174]        SLIDE  VALVES  AND  THEIR  SETTING 


141 


ments  are  being  made.  These  governors  may  change  (a) 
the  valve  travel,  (6)  the  angle  of  advance,  (c)  both  the  valve 
travel  and  the  angle  of  advance.  With  such  governors  the 
eccentric  is  almost  always  fixed  to  the  governor  and  forms  a 
part  of  it.  It  is,  therefore,  not  adjustable  on  the  shaft.  The 
valve-stem  length  should  be  adjusted  for  equality  of  leads 
(Sec.  167)  or  for  a  slightly  larger  lead  at  the  crank  than  at 
the  head  end  (Sec.  169).  If  the  eccentric  must  be  shifted  to 
obtain  satisfactory  operation,  it  is  usually  necessary  to  cut  a 


Governor  Blocked  In 
Full-Load 
Running 
Position 


.•Excess  ive- 
Speed 

>sif/on 


Fia.     193. — Shaft  governor  blocked  in  full-load  running  position  for  adjusting  valve. 


new  flywheel  key  way  into  the  shaft.  Whenever  adjustment 
of  the  eccentric  is  made,  it  should  be  made  only  when  the 
governor  is  " blocked"  (Fig.  193)  into  the  position  which  it 
occupies  when  running  under  full  load  or  that  fraction  of  full 
load  at  which  the  engine  is  most  often  used.  Generally, 
three-fourths  to  full  load  position  is  used.  The  valve  may 
then  be  set  by  the  methods  of  Sec.  167  to  Sec.  169.  See  also 
preceding  Sec.  164. 

NOTE. — To  FIND  THE  FULL-LOAD  RUNNING  POSITION  OF  A  SHAFT 
GOVERNOR,  of  a  type  which  changes  the  valve  travel,  run  the  engine  under 
a  constant  full  load  at  the  proper  speed.  Then,  with  a  scale,  measure  the 
valve-stem  travel.  Now  stop  the  engine  and  so  block  the  governor 
(Fig.  193)  that  the  same  valve  travel  occurs,  when  the  engine  is  turned 
over  by  hand,  as  that  which  occurred  when  the  engine  was  running. 


142    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 


I -First  Set 


175.  The  Steam-Engine  Indicator  Is  Often  Used  In  Valve- 
Setting  Operations  (Figs.  194  to  202).  See  Div.  3  for  a  pre- 
liminary discussion  of  the  application  of  the  indicator  in  valve 
setting.  The  indicator  may  be  used  simply  to  check  the 
setting  of  valves,  which  have  already  been  set  by  measure- 
ment, or  it  may  be  used  to  set  the  valves  approximately  when 
it  is  inconvenient  to  remove  the  valve  chest  cover.  There  are 

two  fundamental  principles 
which  should  be  observed  when 
using  the  indicator  for  valve 
setting:  (1)  The  angle  of  ad- 
vance, or  position  of  the  eccen- 
tric with  respect  to  the  crank, 
determines  the  timing  of  the 
events.  (2)  The  length  of  the 
valve  stem,  or  position  of  the 
valve  on  the  valve  stem,  deter- 
mines the  relative  sizes  (areas) 
of  the  cards  from  each  end  of 
the  cylinder  with  respect  to  each 
other.  A  valve  stem  of  incor- 
rect length  will  produce  an 
effect  on  the  crank-end  card 
opposite  from  that  which  it 
produces  on  the  head-end  card. 
In  other  words,  if  the  crank-end 
card  is  found  to  be  increasing  in 

size  with  each  change  of  length  of  the  valve  stem,  it  will  also 
be  found  that  the  head-end  card  is  correspondingly  decreasing 
in  size.  Shifting  the  eccentric,  however,  will  produce  the  same 
effects  on  both  the  head-end  and  crank-end  diagrams. 


H-Second   Set 


HI-  Final   Sst 

FIG.  194. — Typical  successive  cards 
taken  from  an  engine  while  setting  the 
valves  with  an  indicator. 


EXAMPLE. — The  First  Set  of  cards,  7  (Fig.  194),  taken  from  an  engine 
which  needs  valve  adjustment,  indicate  two  things:  (1)  The  head-end 
and  crank-end  cards  are  not  the  same  size;  therefore  the  valve-stem  length 
must  be  adjusted.  (2)  All  events,  admission,  release,  etc.,  are  late,  and  there- 
fore the  eccentric  must  be  shifted  on  the  crank  shaft.  Since  the  head-end 
card  is  the  smaller,  the  valve  stem  should  be  shortened  to  allow  more 
steam  to  flow  into  the  head-end  of  the  cylinder  and  thus  increase  the  size 
of  the  head-end  card.  Since  all  events  are  late  it  is  necessary  to  increase 


SEC.  175]        SLIDE  VALVES  AND  THEIR  SETTING 


143 


Lengthen 
Valve  Stem 


FIG.  195. — Illustrating  defective  slide- 
valve  setting — valve  stem  too  short 
(outside-admission  valve). 


Lengthen 
Valve  Stem. 
Move 
Eccentric  Ahead 


FIG.  196. — Illustrating  defective  slide- 
valve  setting — valve  stem  too  short. 
(Outside-admission  valve.) 


Events 
Occurring  Late 


Move 
Eccentric  Ahead 


FIG.  197. — Illustrating  incorrect  an- 
gular advance — events  occurring  late. 
(Outside-admission  valve.) 


Events 
Occurring  Early 


Move 
Eccentric  Back 


FIG.  198. — Illustrating  incorrect  an- 
gular advance — events  occurring  early. 
(Outside-admission  valve.) 


Incorrect  Length 
of  Valve  Stem. 
Eccentric 
Improperly  Located 


H.E. 


Lengthen 
Valve  Stem. 
Move  Eccentric 
Forward 


FIG.  199. — Illustrating  defective  valve 
setting — valve  stem  too  short  and  eccentric 
too  far  back.  (Outside-admission  valve.) 


Incorrect  Length  of 
Valve  Stem. 
Eccentric 
Improperly  Located 


Shorten 
Valve  Stem. 
Move 
Eccentric  Back 


FIG.  200. — Illustrating  defective  valve 
setting — valve  stem  too  long  and  eccen- 
tric too  far  ahead.  (Outside-admission 
valve.) 


Events 
Occurring  Early 


Move 
Eccentric  Back 


FIG.  201. — Illustrating  incorrect  an- 
gular advance — events  occurring  early. 
(Outside-admission  valve.) 


Events 
Occurring  Late 


Move 

Eccentric  Aheacf 


FIG.  202. — Illustrating  incorrect  an- 
gular advance — events  occurring  late. 
(Outside-admission  valve.) 


144    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  4 

the  angle  of  advance,  or  shift  the  eccentric  ahead  a  trifle  to  cause  the 
events  to  come  earlier. 

The  Second  Set  of  cards,  II  (Fig.  194),  taken  after  the  above  adjust- 
ments have  been  made,  show  that  the  length  of  valve-stem  is  now  correct 
but  that  the  eccentric  has  been  shifted  too  far  ahead  and  that  all  events 
are  occurring  too  early.  The  eccentric  should  therefore  be  shifted 
backward  about  half  the  amount  by  which  it  was  originally  shifted 
forward. 

The  Final  Set  of  cards,  III  (Fig.  194),  indicate  that  the  valve  is  now 
functioning  properly  and  that  further  adjustments  are  unnecessary. 

176.  Various  Defects  Of  Slide-Valve  Settings,  As  Deter- 
mined By  The  Steam  Engine  Indicator,  And  Their  Remedies 
are  shown  in  Figs.  195  to  202.  See  also  Sec.  112  in  Div.  3  for 
further  information  relating  to  this  subject.  Much  time  will 
be  saved  if  each  set  of  cards  which  is  taken  is  studied  very 
carefully  before  resetting  the  valve.  It  sometimes  happens 
that  successive  cards  will  show  only  slight  changes  in  the  valve 
setting.  It  should  also  be  noted  that  the  various  changes 
recommended  to  correct  the  defective  valve  settings  in  Figs. 
195  to  202  are  only  for  outside-admission  slide  valves.  If 
inside-admission  slide  valves  are  to  be  considered,  adjust- 
ments different  from  those  recommended  in  these  illustrations 
should  be  made;  see  note  following  Table  159. 

QUESTIONS  ON  DIVISION  4 

1.  What  are  the  outstanding  features  of  slide  valves?     On  what  classes  of  engines  are 
they  used? 

2.  What  is  meant  by  valve  setting? 

3.  What  are  valve  diagrams  and  what  is  their  use? 

4.  Enumerate  the  functions  of  a  slide  valve? 

5.  What  are  the  positions  of  the  valve  on  its  seat  and  of  the  piston  in  the  cylinder  at 
admission,  cut-off,  release,  and  compression  for  each  end  of  the  cylinder?     Draw  a  sketch 
for  each  position. 

6.  Explain,  with  a  sketch,  outside-admission  and  inside-admission  slide  valves. 

7.  Enumerate  the  advantages  and  disadvantages  of  plain  D-slide  valves. 

8.  What  are  the  advantages  and  disadvantages  of  piston  slide  valves. 

9.  Do  inside-admission  valves  have  any  advantage  over  outside-admission  valves? 

10.  Draw  a  sketch  to  explain  the  principle  of  balancing  a  flat  slide  valve.     What  is 
the  purpose? 

11.  Summarize  the  advantages  and  disadvantages  of  balanced  slide-valves. 

12.  Discuss  the  merits  of  multiporting  a  valve.     Are  multiported  valves  balanced? 

13.  Explain  the  principle  and  purpose  of  the  riding- cut-off  valve.     Give  its  advan- 
tages and  disadvantages. 

14.  Define  valve  lap.     Draw  sketches  to  differentiate  between  steam,  exhaust,  inside 
and  outside  lap. 

15.  With  inside-admission  valves,  what  other  name  can  be  given  to  the  outside  lap? 
To  the  inside  lap? 


SEC.  176]        SLIDE  VALVES  AND  THEIR  SETTING  145 

16.  What  is  meant  by  inside  clearance?     What  class  of  slide  valves  may  have  inside 
clearance?     What  does  it  accomplish? 

17.  Should  valve  lap  ever  be  changed?     If  so,  when  and  how? 

18.  What  are  the  purposes  of  fitting  a  valve  with  lap? 

19.  Draw  a  sketch  to  define  lead.     Explain  fully  its  purpose. 

20.  What  is  the  usual  operating  mechanism  for  a  slide  valve? 

21.  Explain  the  similarity  of  an  eccentric  to  a  crank.     Is  there  any  difference? 

22.  Define  eccentricity,  eccentric  circle,  throw,  valve  travel. 

23.  What  is  the  usual  relation  of  valve  travel  to  eccentricity? 

24.  Define  the  angle  of  advance.     Upon  what  does  it  depend? 

25.  Explain  the  relative  positions  on  the  shafts  of  eccentrics  for  inside-  and  outside- 
admission  valves. 

26.  With  a  sketch,  illustrate  connecting-rod  angularity.     How  does  it  affect  (1)  the 
piston  velocity,  (2)  the  valve  events? 

27.  Discuss  angularity  of  the  eccentric  rod. 

28.  Define  dead  center  and  tell  why,  in  valve-setting,  it  must  be  accurately  established. 
Give  the  usual  method  of  establishing  dead  centers. 

29.  How  can  one  compensate  for  lost  motion  in  establishing  dead  centers? 

30.  What   are  the  two  general  methods  of  setting  steam-engine  valves?     What  are 
the  advantages  and  limitations  of  each? 

31.  Draw  a  sketch  and  with  it  explain  the  indirect-measurement  method  of  ascertaining 
valve  operation. 

32.  Explain  the  use  of  templets  in  valve  setting. 

33.  With  sketches  describe  how  an  eccentric  can  be  placed  exactly  on  "center." 

34.  What  are  the  possible  adjustments  of  a  slide-valve  operating  mechanism? 

35.  How  should  the  valve  be  set  on  a  new  engine?     On  an  old  engine? 

36.  For  what  three  operating  conditions  may  slide  valves  be  set?     What  are  the 
advantages  of  each  condition? 

37.  How  could  you  proceed  in  setting  a  slide  valve  for  equal  leads? 

38.  Give  the  principal  steps  in  setting  a  valve  for  equal  cut-offs.     Is  this  a  direct 
procedure?     Has  it  any  limitations? 

39.  What  is  the  reason  for  sometimes  setting  a  slide  valve  for  unequal  leads  and  how 
is  it  done? 

40.  Does  setting  for  unequal  leads  provide  an  ideal  indicator  diagram?     Why? 

41.  Does  the  setting  of  multiported  valves  involve  any  more  operations  than  that  of 
single-ported  valves?     Why? 

42.  How  would  you  set  the  main  valve  of  a  riding-cut-off  engine? 

43.  Tell  how  to  set  the  riding-cut-off  valve  of  an  engine  on  which  a  hand-wheel 
adjustment  exists.     How  far  ahead  of  the  crank  should  the  eccentric  be  placed? 

44.  What  is  the  procedure  in  setting  a  riding-cut-off  valve  which  is  controlled  by  a 
shaft  governor? 

45.  How  is  the  riding-cut-off  valve  set  when  it  is  neither  hand-adjustable  nor  governor- 
operated? 

46.  Does  a  shaft  governor  affect  the  procedure  in  valve  setting ?     Why  ? 

47.  Is  it  generally  possible  to  set  a  shaft-governed  engine  for  any  desired  condition? 
Why? 

48.  How  do  throttling  governors  affect  valve  setting? 

49.  How  may  one  find  the  full-load  running  position  of  a  shaft  governor? 

50.  How  do  the  angle  of  advance  and  effective  length  of  valve  stem,  if  incorrect,  distort 
an  indicator  diagram? 

51.  What  would  be  the  procedure  in  rectifying  the  diagrams  shown  in  Fig.  101? 

52.  Describe  the  valves  and  valve-operating  mechanism  of  the  Mclntosh  &  Seymour 
engine. 


10 


DIVISION  5 
CORLISS  AND  POPPET  VALVES  AND  THEIR  SETTING 

177.  The  Reasons  For  Employing  Corliss  Or  Poppet  Valves 

are:  (l)  These  valves  are  suited  to  engines  which  require  small 
clearances,  Sec.  305;  these  valves  can  be  located  very  near  to 
the  place  where  steam  enters  or  leaves  the  cylinder  and  usually 
have  but  a  very  limited  movement.  (2)  They  are  well  adapted 
where  a  quick  opening  and  closing  of  the  valves  is  necessary — 
especially  where  a  quick  closing  of  the  valve  at  cut-off  is 
essential.  (3)  By  reason  of  their  limited  movement,  these  valves 
are  subjected  to  little  friction;  the  mechanical  losses  (Sec.  11)  of 
such  engines  are,  therefore,  small  and  the  valves  will  operate  a 
long  time  without  showing  signs  of  wear. 

NOTE. — ENGINES  WITH  CORLISS  AND  POPPET  VALVES  ARE  USUALLY 
MUCH  MORE  EFFICIENT  (see  Div.  10)  than  are  engines  with  slide  valves, 
but  to  provide  the  increased  efficiency  the  engines  must  have  a  greater 
number  of  parts  and  cost  much  more  to  construct.  They  are  therefore 
used  chiefly  when  the  saving  due  to  their  efficiency  more  than  offsets  their 
high  initial  cost. 

178.  The  Advantages  Of  Corliss  Valves  (see  Div.  2  for 
definition)  are:  (1)  The  valves  may  be  made  to  move  slowly  and 
but  little  when  they  are  opened  or  closed.     (2)   The  valves 
move  rapidly  while  opening  or  closing,  especially  where  detach- 
ing valves  are  used.     (3)  The  valves  may  be  located  very  near  to 
where  the  steam  is  to  be  admitted  to  or  exhausted  from  the  cylinder. 

(4)  The  valve  events — admission,  cut-off,  release,  and  compres- 
sion— are  independently  adjustable,  and  only  cut-off  need  be 
varied  to  meet  the  requirements  of  different  engine  loads. 

(5)  Steam  is  exhausted  from  the  cylinder  through  separate  valves 
from  those  through  which  the  steam  is  admitted.     Thus,  the 
cooler  exhaust  steam  does  not  sweep  over  and  cool  the  admis- 
sion valves;  see  Sec.  274. 

179.  Typical  Designs  Of  Corliss  Valves  are  shown  in  Figs. 
203  to  206,  and  233.     Features  which  distinguish  good  design 
may  be  enumerated  thus:  (1)  The  valves  should  never  extend 

146 


SEC.  179] 


CORLISS  AND  POPPET  VALVES 


147 


into  the  displacement  volume;  that  is,  there  should  be  no  danger, 
even  if  the  valve  were  stopped  in  any 
position,  of  the  piston  striking  it  and 
causing  damage.  (2)  The  valves  should, 
in  all  positions,  be  supported  on  the  seat 
throughout  their  entire  length;  that  is, 
there  should  be  no  tendency  for  the 
steam  acting  on  one  side  of  the  valve 


Edge. 


,5tiffening 
•'  \  Bridges 


Cylinder    , 

Head  "'Exhaust.' 
Valve 

FIG.  203.  —  Corliss  valves 
(positively-operated)  in  cylin- 
der head  of  the  "Ideal"  Cor- 
liss-valve engine. 


**-Slot  For  Valve 
Gear  Engagement 

FIG.  204. — Corliss   admission   valve   of   the  "Ideal" 
Corliss-valve  engine. 


Admission  Valve 


I-  Hamilton 
Type  Valve 


H  -  Ty  pe 

Frequently  Used 


FIG.  205. — Detaching  Corliss-engine  admission  valves  (Hooven,  Owens,  Rentschler 
Company.  Valve  V\  is  supported  its  full  length  at  all  times.  Valve  Vz,  when  open,  is 
supported  only  at  its  ends  or  by  the  bridges  which  may  cause  it  to  spring.  V\  weighs 
somewhat  less  than  Vi.  The  cylinder  clearance  is  somewhat  less  with  Vi  than  with  F2.) 


,Cap 


Piston 
Ring-. 


.-Piston 


Exhaust  Valve 
I-  Hamilton 
Exhaust  Valve 


Type  of  Exhaust 
Valve  Frequently 
Used 


FIG.  206. — Detaching  Corliss-engine  exhaust  valves.  (Hooven,  Owens,  Rentschler 
Co.  In  the  Hamilton  cgnstruction,  Vi,  the  valve  does  not  rock  into  the  cylinder  space, 
where,  should  the  valve  gear  break,  it  might  wreck  the  engine.) 


to  bend  it  and  thus  possibly  cause  uneven  wear  of  its  seat. 


148    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 


SEC.  180] 


CORLISS  AND  POPPET  VALVES 


149 


(3)  With  multiported  valves,  the  number  of  edges  past  which 
leakage  might  occur  should  be  a  minimum.  (4)  The  total  pro- 
jected area  against  which  steam  may  act  to  force  the  valve  against 
its  seat  should  be  a  minimum,  so  as  to  reduce  the  force  causing 
friction  at  the  valve. 

180.  Positively-Operated  Corliss-Valve  Mechanisms  are 
illustrated  in  Figs.  38,  207,  208,  209,  and  235.  The  admission 
valves  in  these  mechanisms  are  usually  operated  through  a 
wrist  plate  (Fig.  38)  or  through  a  system  of  separate  levers  and 
links  for  each  valve: — these  levers  may  be  located  at  the  valve 


l-Central  Position  II- Extreme  Position 

FIG.  208. — Showing  linkwork  inside  of  gear  case  of  Ridgway  four-valve  engine. 

(Fig.  209)  or  alongside  the  crosshead  guides  (Fig.  207),  and 
they  may  be  enclosed  in  a  dust-proof  case  or  they  may  be 
exposed.  The  valves  may,  however,  be  driven  by  rods 
attached  directly  to  a  rocker  arm  as  are  the  exhaust  valves 
in  Fig.  209.  The  exhaust  valves  are  usually  driven  from  a 
separate  wrist  plate  or  directly  from  a  rocker  arm,  although 
they  are  sometimes  driven  by  a  system  of  levers  and  links  such 
as  that  shown  for  the  admission  valves  in  Fig.  209. 

181.  The  Advantages  And  Disadvantages  Of  Positively- 
Operated  Corliss-Valve  Engines  are,  in  general,  those  stated 
in  Sec.  178.  The  following  additions  should  be  noted:  (1) 
Being  positively-operated,  the  valves  may  be  operated  at  higher 


150    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

speeds  than  can  the  detaching  Corliss  valves.  This  means  that, 
with  a  given  size  of  cylinder,  a  positively-operated-valve 
engine  may  operate  at  a  higher  speed  and  hence  can  develop 
more  power  and  can  operate  satisfactorialy  with  a  smaller 
flywheel  than  can  an  engine  which  has  detaching  valves. 
(2)  The  operation  of  the  valves  is  practically  noiseless.  Detach- 
ing Corliss  engines  make  considerable  noise  as  the  dash  pots 
close.  (3)  Shaft  governors  are  more  applicable  to  positively- 


Oil   Trouqh                                J 

1 

f  .     d:i  |                                      |3  -j;j| 

Base 

Fia.  209. — Valve  gear  of  Ames  four-valve  non-releasing  Corliss  engines.     (Ames  Iron 

Works.) 


operated  than  to  detaching  valves.  This  means  that  the 
speed  regulation  will,  generally  speaking,  be  better  with  posi- 
tively-operated valves.  (4)  For  long-stroke,  slow-speed 
engines  especially,  positively-operated  valves  do  not  give  as  quick 
cut-off  as  do  the  detaching  valves.  It  follows  from  the  above 
that  positively-operated  Corliss  valves  are  best  suited  for 
short-stroke,  medium-  and  high-speed  engines  where  close 
regulation  of  speed  is  desired.  They  provide  a  relatively 
compact,  efficient,  and  noiseless  type  of  engine  for  this  service. 


SEC.  181] 


CORLISS  AND  POPPET  VALVES 


151 


152    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Dnr.  5 


182.  Detaching  (Releasing,  Or  Drop-Cut-Off)  Corliss- 
Valve  Mechanisms  (see  Sec.  50  for  definition)  are  illustrated 
in  Figs.  210  to  212.  The  valve  stem,  S,  Fig.  211,  is  extended 
from  the  cylinder  through  a  bracket  or  bonnet  and  has  keyed  to 
it  the  steam-valve  arm  (D,  Fig.  212).  The  hub  of  the  steam- 


.•Bonnet 


Governor  Cam  Rod--. 
Knock-Off 

Lever-^ 
Bel  I  I 

{Crank—.     \ 

'      xt>? 


Earliest  Cut-Off-. 
Knock-Off 

Lever-.          \ 
Knock-Off 

Cam-.^ 
Spring-.     ''• 


Latest  Cut-Off 
Governor 
Rod-. 


Steam- 
Valve 
Arm 


FIG.     211. — Part-side    view    of    typical 
Corliss-valve  releasing  mechanism. 


/_..  -Safety 

Cam 
''Steam-Valve 
Arm 


Rod 


FIG.     212.  —  Front    view    of    typical 
Corliss-valve  releasing  mechanism. 


valve  arm  forms  a  shaft  upon  which  a  bell  crank,  B,  Fig.  212, 
and  a  knock-off  lever,  E,  are  mounted  so  as  to  turn  freely.  B  is 
connected  at  one  end  to  the  steam-valve  rod  (K,  Fig.  210) ;  and 
carries  at  its  other  end  a  latch  or  hook  (C,  Fig.  212)  which  is 
pivoted  at  A.  The  steam-valve  arm,  D,  has,  attached  to  it, 


Safety  Cam-' 

Steam  Arm  -  - 1' 
Dash-Pot  Rod-^, 
I-Lcntch  Raising  Valve  H- Latch  Released 

FIG.  213. — The  Reynolds  trip  gear  for  Corliss  engines. 

a  dash-pot  rod  (Z),  Fig.  210)  which  leads  to  a  dash  pot,  X. 
The  operation  of  this  releasing  mechanism  or  trip  gear  is 
explained  below: 

EXPLANATION. — Suppose  the  bell  crank  to  be  turned,  by  the  steam- 
valve  rod,  in  the  direction  indicated  in  Figs.  212  and  213.     The  latch,  C, 


SEC.  183]  CORLISS  AND  POPPET  VALVES  153 

engages  a  projection  or  catch  plate,  P,  on  the  steam-valve  arm,  D,  and 
raises  D,  rotating  it  about  its  axis  and  opening  the  valve.  The  dash-pot 
rod  is  also  raised,  forming  a  partial  vacuum  in  the  dash  pot.  Arms  B  and 
D  thus  turn  together  as  one,  until  the  inner  arm  of  the  latch  strikes  the 
knock-off  cam  on  the  lever,  E,  which  remains  stationary.  When  the 
latch  arm  does  strike  the  knock-off  cam — lever  B  still  moving  as  indi- 
cated— the  latch  is  rotated  about  its  pivot  at  A  and  the  catch  plate  on  D 
is  released  from  the  hook,  C.  The  air  pressure  above  the  dash-pot  piston 
immediately  forces  it  down,  drawing  arm  D  with  it  and  closing  the  valve. 

183.  Advantages  And  Disadvantages  Of  Detaching-Corliss- 
Valve  Engines  are,  generally,  as  given  in  Sec.  178,  and  in 
addition,  the  following:  (1)  Cut-off  occurs  very  rapidly  irrespec- 
tive of  the  engine  speed  or  load.     This  makes  these  valves 
satisfactory   for   slow-speed,   long-stroke   engines,    of   which 
class  all  very  large  engines  necessarily  must  be.     (2)    The 
valves  cannot  be  operated  at  high  speed  because,  at  high  speeds, 
the  valves  tend  to  act  sluggishly  and  sometimes  do  not  open. 
(3)    The  valve  mechanism  is  noisy  as  compared  to  that  of 
positively-operated   Corliss   valves.     From   the   above   it   is 
evident    that    the     detaching-Corliss-valve     mechanism     is 
particularly  and  well  suited  to  large  low-speed,  long-stroke 
engines. 

184.  The  Elements  Of  A  Detaching-Corliss-Valve  Mechan- 
ism are,  besides  the  releasing  or  trip  gear  described  in  Sec.  182, 
the  following:   (1)  An  eccentric,  E,  Fig.  210,  for  imparting 
motion  to  the  valve  gear.     (2)  A  wrist  plate,  W,  which  receives 
the  motion  of  the  eccentric  and  imparts  it  to  (3)  the  valve 
rods,  K  and  L,  which  in  turn  move  the  bell  cranks,  B,  Fig. 
212,  and  the  exhaust-valve  arms.     Since  the  distance  from  the 
eccentric  to  the  wrist  plate  is  long,  the  connection  between 
them  is  made  up  of  (4)  an  eccentric  rod,  P,  Fig.  210,  and  (5) 
a  reach  rod,  Q,  both  supported  on  a  (6)  rocker  arm,  R,  which 
relieves  the  wrist  plate  and  eccentric  of  considerable  weight. 
The  knock-off  levers,  E,  Fig.  212,  are  held  in  place  by  (7) 
governor  rods,  H,  Fig.  210,  which  are  controlled  through  a  bell- 
crank  lever,  B,  by  the  (8)  governor  drop  rod,  0.     (9)  The  dash 
pot  rod,  D,  Fig.  210,  connects  the  steam  valve  arm,  D,  Fig. 
212,  with  the  (10)  dash  pot  piston  in  X,  Fig.  210. 

NOTE. — DETACHING-CORLISS-VALVE  ENGINES  FREQUENTLY  HAVE  Two 
ECCENTRICS  and  then,  of  course,  they  also  have  two  eccentric  rods, 


154     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

two  rocker  arms,  two  reach  rods,  and  (usually)  two  wrist  plates.  The 
reason  for  using  two  eccentrics  is  explained  in  Sec.  185.  Furthermore, 
engines  of  certain  makes  depart  somewhat  from  the  exact  mechanism 
described  above  but  these  are  special  constrictions  which  are  so  designed 
for  some  specific  purpose  and  usually  differ  very  little  from  that  here 
described. 

185.  The  Features  Of  Single-  And  Double-Eccentric 
Detaching-Corliss- Valve  Mechanisms  are:  (1)  When  a 
single  eccentric  drives  both  the  steam  and  the  exhaust  valves, 
the  range  of  cut-off  is  limited  to  about  one-third  the  piston  stroke. 
The  reason  for  this  is  explained  below.  (2)  In  order  to  obtain 
a  greater  range  of  cut-off,  separate  eccentrics  are  employed,  one 
to  drive  the  exhaust  valves,  the  other  to  drive  the  steam 
valves.  With  two  eccentrics,  the  admission  and  exhaust 
valves  can  be  adjusted  independently,  and  steam  may  be  cut 
off  anywhere,  nearly  to  the  end  of  the  stroke. 

EXPLANATION. — WHY,  WITH  A  SINGLE  ECCENTRIC,  THE  CUT-OFF 
RANGE  Is  LIMITED  To  ABOUT  ONE-THIRD  STROKE  may  be  explained  thus: 
After  an  eccentric,  in  rotating,  reaches  the  extreme  of  its  throw  or  its 
"center"  position  (Sec.  154),  all  of  the  motions  which  it  compels  are 
reversed.  Now,  in  a  Corliss  trip  gear,  the  catch  plate  is  released — if 
released  at  all — while  the  wrist  plate  pulls  on  the  bell  crank.  Also,  the 
wrist  plate  ceases  to  pull  on  a  bell  crank  when  its  direction  of  rotation  is 
reversed;  that  is,  when  the  eccentric  from  which  the  wrist  plate  derives 
its  motion  reaches  its  center  position.  Therefore,  the  catch  plate  is 
released — if  released  at  all — before  the  eccentric  reaches  the  extreme  of 
its  throw.  Now,  considering  the  eccentric  motion  with  reference  to  the 
exhaust  valves,  which  it  also  operates  through  the  wrist  plate — it  is 
evident  that  each  exhaust  valve  has  its  greatest  opening  when  the  wrist 
plate,  and  hence  the  eccentric,  is  in  its  extreme  position.  It  is  also 
evident  that  the  exhaust  valve  opens  and  closes  at  equal  time  intervals 
before  and  after  it  has  its  greatest  opening.  Therefore,  since  release  must 
occur  before  the  end  of  a  forward  stroke  and  since  compression  (exhaust 
valve  closure)  must  occur  befoVe  the  end  of  a  return  stroke,  it  is  evident 
that  the  greatest  opening  of  the  exhaust  valve,  and  hence  the  extreme 
throw  of  the  eccentric,  must  occur  before  the  middle  of  the  return  stroke. 
It  follows,  then,  that  the  eccentric  must  occupy  its  other  extreme  position 
before  the  middle  of  the  forward  stroke.  Now,  since  the  steam  valves — 
if  released  at  all — must  be  released  before  the  eccentric  reaches  its  extreme 
position,  it  follows  that  they  must  be  released  before  one-half  stroke  is 
completed. 

It  follows  from  the  above  that,  to  obtain  as  large  a  cut-off  range  as 
possible  with  a  single-eccentric  mechanism,  both  release  and  exhaust  valve 


SEC.  186] 


CORLISS  AND  POPPET  VALVES 


155 


closure  must  occur  late.  These  conditions  might  be  satisfactory  for  a 
very  slow  rotative  speed;  but,  for  higher  speed,  earlier  release  and  more 
compression  would  surely  be  required.  These  latter  conditions  can  only 
be  obtained  by  moving  the  eccentric  forward  on  the  shaft,  and  this  in 
turn  cuts  down  the  cut-off  range.  The  practical  cut-off  range  with  a 
single-eccentric  Corliss-valve  mechanism  is  therefore  about  one-third 
stroke. 

186.  Typical  Designs  Of  Corliss-Valve  Detaching  Mechan- 
isms Or  Trip  Gears  are  shown  in  Figs.  211,  212,  and  214  to 


Governor 
Valve          Toe 
Bracket- 


.  -  -Rod  To  Governor 

Toe  Collar 

"7-Governor- Toe  Collar 
Knock-Off  Lever 
'Safety 
Cam      lir-^l  .-Latch 

-Latch 
Plates 


•Steam 
Valve  Rod 


FIG.  214. — Gravity  trip  gear  of  Hamilton  Corliss  engines. 

221.  The  Reynolds  trip  gear,  as  shown  in  Figs.  211,  212  and 
220,  is  probably  the  oldest  design  and  most  widely  used.  It 
relies  upon  a  spring  to  cause  engagement  of  the  hook  and  catch 
plate.  Because  springs  sometimes  break,  some  manufacturers 
have  designed  trip  gears  in  which  engagement  is  effected  by 
gravity  (Figs.  214  and  219).  Other  manufacturers  employ 
positive  knock-off  cams  (Figs.  215  and  216)  which  have  an 
added  advantage  of  being  adapted  to  somewhat  faster  opera- 
tion than  either  spring-  or  gravity-opposed  cams. 

187.  Dash  Pots  For  Detaching  Corliss  Valves  (Fig.  222)  are 
constructed  differently  by  almost  every  manufacturer.     The 


156    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 


Governor-. 


-•Safety  Device 


\Wrist  Plate 

FIG.  215. — Nordberg  long-range  valve  gear  and  governor.  (The  main  lever,  A, 
is  supported  by  a  bracket  on  the  governor  at  point  P  about  which  it  is  caused  to  swing 
by  the  knock-off  eccentric  rod,  E.  At  the  bottom  end  of  this  lever  is  hung  the  three- 
armed  lever,  K,  the  two  vertical  ends  of  which  are  connected  to  the  knock-off  cams  and 
the  horizontal  arm  is  connected  by  the  drop  rod  to  the  governor  at  point  Pz.  The  drop 
rod  is  parallel  to  A.  It  is  obvious  that  since  this  parallelogram  is  oscillated  by  the 
knock-off  eccentric  drive  rod,  its  sides  must  remain  parallel;  therefore,  the  lever,  K, 
always  moves  in  a  position  parallel  to  itself.  Should,  however,  a  change  of  load  occur, 
the  governor  then  lifts  or  lowers  the  point,  Pz,  thus  changing  the  angularity  of  lever  K  and 
changing  the  center  of  oscillation  of  the  cams  and  the  point  of  cut-off.) 


.-BellCmnk 

.-Catch  Plate 
••'    .••  Bonnet 


Cam 


Dash- 

Pot  Rod - 


FIG.  216. — Patent  long  range  Corliss  trip 
gear.      (Nordberg  Mfg.  Co.) 


Bonnet 


Bell 
Crank 


Dash-Pot  Rod 


FIG.  217. — Corliss-valve  trip  gear  as  used 
on  Vilter  engines., ^  (Vilter  Mfg.  Co.) 


SEC.  187] 


CORLISS  AND  POPPET  VALVES 


157 


primary  function  of  the  dash  pot  is,  of  course,  to  provide  a 
means  for  quickly  closing  the  admission  or  steam  valve  when 
the  catch  plate  is  released  from  the  hook.  A  dash  pot  which 
was  designed  to  produce  only  this  effect  might,  however, 
cause  much  noise  when  the  plunger  struck  the  bottom  of  the 
cylinder.  To  overcome  this  objectionable  feature,  dash  pots 
are  usually  equipped  with  a  secondary  piston  which  must 
force  air  from  a  cylinder  as  it  descends.  By  properly  restrict- 

.  •  Go  vernor  Rod 

^^  Knock-Off 
: 'Lever 

Si-earn  Valve 
Arm- 


Knock-Off 
Bar-, 


Knock- 
Off 
Cam-- 
Latch 

Latch 
Pivot 
Point-' 
Catch 
Plate 
Bell     f, 
Crank' ' 


FIG.    218. — Vilter  Corliss-engine  trip 
gear  showing  knock-off  bar. 


Steam- 
Valve  Rod 


FIG.  219. — Gravity  trip  gear  of  Murray 
Corliss  engines.  (Murray  Iron  Works 
Co.) 


ing  the  opening  through  which  the  air  is  expelled,  a  very  effect- 
ive cushion  can  thus  be  provided. 

EXPLANATION. — As  explained  in  Sec.  182,  when  the  dash  pot  is  lifted 
through  rod,  R  (Fig.  222),  a  partial  vacuum  is  created  beneath  the  piston, 
P.  Also,  air  is  drawn  in  through  the  hole,  H,  into  the  lower  portion  of 
cylinder  C.  When  the  dash-pot  rod  is  released,  the  air  pressure  from 
above  forces  down  the  plunger,  which  must  now  displace  the  entrapped 
air  from  C.  The  passage  of  air  from  C  is  restricted  by  the  valve,  V, 
which  can  so  be  adjusted  as  to  produce  in  C  the  desired  cushioning. 

NOTE. — THE  TRIP  GEAR  SHOULD  PROVIDE  A  MEANS  FOR  CLOSING 
THE  STEAM  VALVE  IF  THE  DASH  POT  DOES  NOT  FUNCTION.  With  the 
Reynolds  gear,  the  inside  of  the  hook  C,  Fig.  213,  accomplishes  this  result 
by  forcing  down  the  dash-pot  rod.  With  the  mechanisms  of  Figs.  217 
and  219,  the  steam  valve  is  positively  closed  by  the  pin  A. 


158    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 


SEC.  188] 


CORLISS  AND  POPPET  VALVES 


159 


188.  The  Advantages  And  Disadvantages  Of  Poppet  Valves 

(see  Sec.  51  for  definition)  are:  (1)  They  are  very  well  suited  to 
use  with  superheated  steam;  because  they  are  small  and  very 
symmetrical  in  form,  they  are  not  distorted  by  temperature 
changes.  (2)  A  large  valve  opening  is  effected  with  only  a  small 
valve  movement;  thus,  little  work  is  required  to  move  the  valve 
in  opening  it.  (3)  The  valve  does  not  slide  on  its  seat,  but  lifts 
from  the  seat;  thus,  there  is  no  wear  between  the  two  and  the 
valve  is  not  likely  to  leak.  (4)  The  clearance  can  be  small  as 
with  Corliss  valves;  thus,  clearance  losses  are  kept  small.  (5) 


Bonnet-        .- Knock-Off  Cam 

Governor 
Rod- 


Drop  Rod- , 
Cylinder, 


Cushion 
;'  Space 
\  Adjusting 
Valve. 


Plunger^ 


Plug' 


'Suction  Space 


FIG.     221.  —  Nordberg    standard    Corliss 
valve  gear. 


FIG.  222. — Corliss-valve  dash  pot. 
(Murray  Iron  Works,  Burlington, 
Iowa.) 


Poppet-valve  operating  mechanisms  are  usually  complex;  being 
more  complicated  than  the  mechanisms  for  any  other  type. of 
valve,  they  are  usually  also  more  expensive.  The  use  of 
poppet  valves  in  steam  engines  is  comparatively  recent 
practice.  Many  new  forms  of  valve-operating  mechanisms 
are  being  made  but  whether  all  of  these  mechanisms  are 
mechanically  good  remains  yet  to  be  seen.  (6)  Poppet  valves 
are  nearly  balanced  because  they  expose  only  a  small  unbal- 
anced area  to  steam  pressure;  they  are,  thus,  easily  lifted  from 
their  seats.  The  slight  unbalance  is  really  desirable  as  the 
steam  pressure  holds  the  valves  against  their  seats  and  thus 
prevents  leakage.  The  use  of  poppet  valves  is  certain  to 
continue,  however,  and  increase  as  time  goes  on  and  as  facili- 
ties for  the  production  of  superheated  steam  improve. 


160     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

NOTE. — POPPET  VALVES  SHOULD  BE  So  LOCATED  IN  THE  ENGINE 
CYLINDER  THAT  WATER  CANNOT  STAND  ON  THEIR  SEATS  when  the 
engine  is  not  running.  If  water  is  permitted  to  collect  on  the  valve  seats, 
it  soon  corrodes  them  and  causes  leakage.  The  slightest  leak  affords  a 
place  for  steam  to  blow  through  and  wear  a  larger  leak. 

189.  Single  And  Double-Beat  Poppet  Valves  (Figs.  40  and 
41)  are,  respectively,  those  (Fig.  40)  which  are  solid  and  close 


Dash-pot 
Piston  - 


Thermometer 


FIG.  223. — Longitudinal  section  through  cylinder  of  Vilter  poppet-valve  engine.     (Vilter 

Mfg.  Co.) 

against  one  ring  or  a  seat,  and  those  (Fig.  41)  which  are  made 
hollow  and  close  against  two  rings  or  seats,  one  above  the 
other.  Single-beat  poppet  valves  are  analogous  to  simple 
slide  valves  in  that  they  are  forced  against  their  seats  by  the 
difference  of  the  pressures  above  and  below  the  valve,  and  in 
that  when  open  they  offer  but  one  passage  through  which  the 
steam  can  flow;  Double-beat  poppet  valves  are  analogous 


SEC.  190] 


CORLISS  AND  POPPET  VALVES 


161 


to  balanced,  double-ported  slide  valves  in  that  the  difference 
of  the  pressures  above  and  below  the  valve  acts  only  on  a  por- 
tion of  the  valve's  projected  cross-sectional  area,  and  in  that, 
when  open,  the  steam  may  flow  under  the  outer  edge  and 
through  the  hollow  center  of  the  valve. 

190.  Typical  Designs  Of  Poppet- Valve  Mechanisms  are 
illustrated  in  Figs.  41,  42,  223  to  227,  and  242.  In  general,  it 
may  be  stated  that  the  poppet  valve  is  given  its  motion  by  an 
oscillating  cam  (Figs.  41,  42,  224  and  246)  or  a  reciprocating 


Cam  Lever,  Operated 
From  Eccentric  On 
Crank  Shaft 


Double-beat 

Admission 

Valve 


Exhaust  Pipe-' 


FIG.  224. — Longitudinal   section  through   cylinder   of  Skinner  "Universal  Una-flow" 
engine,  showing  valve-operating  mechanisms. 

cam  (Figs.  227  and  242)  which  in  turn  derives  its  motion 
from  an  eccentric.  The  eccentric  may  be  on  the  main  or 
crank  shaft  of  the  engine  or  it  may  be  on  a  lay-shaft  which  lies 
alongside  of  and  parallel  to  the  longitudinal  axis  of  the  cylinder 
and  which  derives  its  motion  through  miter  or  helical  gears 
from  the  crank  shaft.  The  cam  which  operates  the  valve 
may  be  a  positive  one — that  is,  it  may  compel  the  closure  as 
well  as  the  opening  of  the  valve — or  it  may  simply  open  the 
valve  against  a  spring  which  later  closes  the  valve.  The 
spring,  if  one  is  used,  should  be  located  where  the  high- 
11 


162     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 


•Distance  Between  Tram  Marks 

In  Inches,  Is  Stamped  On  Rod.  Admission  Valve 

.Peep  Hole 
Roller 
Rod 

T 


. 

xhaust  Ring-..         Admission  Valve. 


FIG.  225. — Longitudinal    section   through  cylinder   of  "Ames   controlled-compression 

una-flow"  engine. 


Governor 
Rod-. 


^ 

FIG.  226. — Poppet-valve  operating  mechanism  of  Vilter  engines.  (Note  that  this 
engine  employs  the  usual  double-eccentric  Corliss-valve  trip  gear  for  operating  the 
poppet  valves.) 


SEC;  191] 


CORLISS  AND  POPPET  VALVES 


163 


.Cam -Rod,  Operated 
'.   from  Eccentric 


temperature  steam  will  not  flow  over  it  and  thereby  heat  it. 
A  spring  which  is  subjected  to  high  temperature  is  apt  to 
rapidly  lose  its  temper. 

191.  In  Setting  The  Valves  Of  A  Corliss-  Or  Poppet-Valve 
Engine,  the  first  thing  to  do  is,  if  possible,  to  get  the  manu- 
facturer's instructions  and  recommendations  as  to  the  lap  and 
lead.     If  this  information  can- 
not   be.  obtained,    the    valve- 
setting  may  be  done  as  directed 

in  the  following  sections.  Good 
values  of  steam  lap,  exhaust 
lap,  and  steam  lead  for  Corliss 
engines  are  given  in  Table  193. 

192.  The  Directions  For  Set- 
ting Valves  Of  Single -Eccentric 
Detaching-Corliss-Valve    E  n  - 
gines  are: 

1.  ESTABLISH  MARKS,  if  this  was 
not  previously  done..    The  necessary 
marks  are:  (a)  Three  marks — C,  B, 
and  D,  Fig.  228 — on  the  wrist-plate 
support,  to  denote  the  central  and 
extreme  positions  of  the  wrist  plate. 
(6)    A  mark,  A,  on  the  wrist-plate 
hub,  which  is  used  with  B,  C  and  D. 
(c)  A  mark  or  marks  (S,  Fig.  229)  on 

.  .     FIG.  227.— Detail  of  poppet-valve  mechan- 

the  end  of  each  steam  and  exhaust  ism  on  head  end  of  Chuse  uniflow  engine, 
valve — the  mark  to  denote  the 

position  of  the  valve's  working  or  cutting  edge,  (d)  A  mark  or  marks 
(T,  Fig.  229)  at  the  end  of  each  valve  seat — to  indicate  the  position  of 
the  working  edge  of  the  seat. 

The  mark  A  (Fig.  228)  is  made  at  any  convenient  point  on  the  wrist- 
plate  hub,  usually  on.  the  top  as  shown.  Then,  with  the  wrist  plate  in  its 
vertical  position  (Fig.  230) — that  is,  with  the  reach-rod  pin  directly  in 
vertical  line  with  the  center  of  the  wrist  plate — mark  B  is  located  on  the 
support  opposite  A  which  is  on  the  wrist  plate,  as  shown  in  Fig.  228. 
Marks  C  and  D  are  located  later  as  described  under  (4).  To  make  marks 
S  and  T,  remove  the  back  bonnets  (the  plates  over  the  valve  openings  on 
the  opposite  side  of  the  cylinder  from  the  wrist  plate).  Remove  the 
valves  successively  from  their  seats  and  with  a  straight-edge  along  the 
working  edges  (Fig.  231)  scribe  marks  at  the  ends.  These  marks  can 
then  be  cut  lightly  with  a  cold  chisel  as  shown  in  Fig.  229. 

2.  ADJUST  THE  LENGTHS  OF  THE  STEAM  AND  EXHAUST  VALVE  RODS 


164     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

(K  and  L,  Figs.  210  and  232).  To  do  this,  unhook  the  reach  rod,  Q,  from 
the  wrist  plate  and  set  the  wrist  plate  in  its  central  position,  that  is,  with 
mark  A  opposite  mark  B,  Fig.  228.  Clamp  the  wrist  plate  in  this  posi- 
tion by  placing  a  sheet  of  paper  between  it  and  the  washer,  L  (Fig.  228), 
and  tightening  the  retaining  nut.  Remove  the  back  bonnets,  as  above 
directed,  if  this  was  not  previously  done.  Now  adjust  the  lengths  of  the 


•Corliss  Valve 

Encf 
^  .Cutting  /  of 

,.--'  Edge      ;  Valve 


FIG.  228.- — Plan  view  of  Corliss  wrist 
plate  showing  marks  used  in  setting 
valves. 


FIG.  229. — Showing  marks  on  Corliss 
valve  and  seat  whereby  the  relation  of 
the  cutting  edges  can  be  judged. 


steam  valve  rods,  K,  so  that  the  valves  have  a  little  lap  as  shown  on 
Fig.  233.  These  rods  are  nearly  always  made  with  right  and  left-hand 
threads  at  opposite  ends  to  facilitate  adjustment.  The  lap,  measured 
between  S  and  T  (Fig.  233),  will  range  from  He  to  Y±  in.  for  small  engines 
and  from  ^  to  %  in.  for  larger  engines;  see  also  Table  193.  Then  adjust 

Reach 
Rod-. 


FIG.  230. — Plumbing  wrist  plate  and 
rocker  arm. 


Steel  \  Scribe 

Straight-Edge'-       Hark  *"' 


FIG.  231. — Showing  method  of  making  mark 
on  end  of  a  Corliss  valve. 


the  lengths  of  the  exhaust  valve  rods,  L,  Figs.  210  and  232,  so  that  the 
valves  will  just  coincide,  or — in  other  words — so  that  the  marks  E  and  F, 
Fig.  233,  are  in  line  with  each  other.  Some  engineers  prefer  a  slight 
amount  of  lap  at  the  exhaust  ports  (see  Table  193),  others  prefer  a  slight 
opening  of  the  exhaust  ports  when  the  wrist  plate  is  central;  under  these 
conditions  the  marks  E  and  F  cannot  be  in  line.  The  distance  between 


SEC.  192] 


CORLISS  AND  POPPET  VALVES 


165 


these  lines  will  be  equal  to  the  desired  amount  of  opening  or  lap.     For 
small  engines  the  opening  of  the  exhaust  valves  may  be  He  in.  and  for 


FIG.  232. — Valve  side  of  Fulton  Corliss  engine  cylinder.     (Fulton  Iron  Works  Co., 

St.  Louis.) 


FIQ.  233. — Back  view  of  cylinder  of  Fig.  232  with  valves  shown  in  section. 

large  engines  it  may  be  up  to  %6  in.;  but  in  any  case,  the  amount  of 
this  opening  must  be  less  than  the  lap  of  the  steam  valves,  otherwise  there 
will  be  danger  of  steam  blowing  through  without  doing  work.  When  rods 


166     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

K  and  L  have  been  adjusted,  the  paper  may  be  removed  from  the  wrist 
plate  and  the  reach  rod  fastened  to  it. 

3.  ADJUST  THE  LENGTH  OF  THE  REACH  ROD  (Q,  Figs.  210  and  232). 
To  do  this,  loosen  the  set  screws  which  hold  the  eccentric  to  the  shaft 
and  turn  the  eccentric  on  the  shaft — or,  without  loosening  the  eccentric, 
turn  the  flywheel — until  the  rocker  arm  (R,  Fig.  210)  stands  exactly 
vertical — if  the  flywheel  is  turned,  have  someone  watch  the  clearance 
at  the  upper  ends  of  the  dash-pot  rods  (see  instruction  9).     Use  a  plumb 
line,  employing  the  same  method  as  shown  for  the  wrist  plate  in  Fig.  230, 
to  establish  the  vertical  position.     Fasten  the  eccentric  temporarily  to 
the  shaft  with  a  set  screw.     With  the  rocker  arm,  R,  vertical,  adjust 
the  length  of  the  reach  rod,  Q,  so  that  the  wrist  plate  also  stands  vertical 
or  central — that  is,  with  mark  A  opposite  mark  B  (Fig.  228). 

4.  ADJUST  THE  LENGTH  OF  THE  ECCENTRIC  ROD  (P,  Fig.  210).     Again 
loosen  the  eccentric  set  screws  and  turn  the  eccentric  around  on  the 
shaft — or  simply  turn   the  flywheel — at  the  same   time  watching    (or 
having  someone  watch)  the  movement  of  the  mark  A,  Fig.  228,  with 
respect  to  B.     If  marks  C  and  D  are  already  on  the  wrist-plate  hub, 
A  should  move  exactly  from  C  to  D.     If  no  marks  C  and  D  exist,  A 
should  move  equal  distances  to  both  sides  of  B.     If  A  does  not  move  as 
specified,  adjust  the  length  of  the  eccentric  rod,  P  (Fig.  210),  until  it 
does.     If  there  were  no  marks  C  and  D  (Fig.  228),  they  can  now  be 
established  for  future  use,  at  each  of  the  extreme  positions  of  A. 

5.  SET  THE  ECCENTRIC  ON  THE  SHAFT.     Place  the  engine  on  one  of  its 
dead  centers  (Sec.  153).     Rotate  the  eccentric  on  the  shaft  in  the  direc- 
tion the  engine  is  to  run  until  the  admission  valve  nearest  the  piston 
opens  by  the  desired  lead.     Lead  for  Corliss  engines  may  be  taken  as 
J-^4  to  2»<j2  m-  Per  f°ot  °f  stroke;  see  also  Table  193.     After  the  proper 
lead  has  been  given  to  the  valve,  secure  the  eccentric  to  the  shaft  and 
turn  the  shaft,  the  eccentric  turning  with  it,  in  the  engine's  running 
direction  to  the  opposite  dead  center.     If  the  lead  at  this  end  is  not  the 
same  as  on  the  other  steam  valve,  shorten  or  lengthen  the  connection 
between  the  eccentric  and  the  wrist  plate  but  bear  in  mind  that  much 
adjustment  in  the  length  of  these  connectors  is  not  permissible  without 
resetting  the  valves  with  respect  to  the  wrist  plate.     When  both  valves 
show  the  same  lead,  make  sure  that  the  eccentric  is  securely  fastened  to 
the  shaft. 

6.  ADJUST  THE  LENGTH  OF  THE  GOVERNOR  DROP  ROD  (0,  Fig.  210) 
so  that  it  oscillates  its  bell  crank,  B,  equally  out  of  its  horizontal  position 
when  the  governor  balls  are  brought  into  their  highest  and  lowest 
positions. 

7.  ADJUST  THE  LENGTHS  OF  THE  GOVERNOR  CAM  RODS  (H,  Figs.  210, 
and  232).     Place  the  starting  block  or  stop   (S,  Fig.  247)  under  the 
governor  cross  arm  and,  after  unhooking  the  reach  rod  from  the  wrist 
plate,  turn  the  wrist  plate  until  marks  A  and  C  (Figs.  228)  stand  in  line. 
The  head-end  steam  valve  should  now  be  wide  open.     Adjust  the  length 


SEC.   192] 


CORLISS  AND  POPPET  VALVES 


167 


of  the  head-end,  or  longer,  cam  rod  so  that  the  catch  blocks  are  almost 
ready  to  separate  for  this  governor  position.  Move  the  wrist  plate  to  its 
other  extreme  position  and  adjust  the  other  governor  cam  rod  in  the  same 
way.  If,  now,  a  H  in.  thick  piece  of  wood  or  iron  is  placed  between  the 
governor  block  and  the  governor  cross  arm,  the  steam  valves  should  be 
both  released  as  the  wrist  plate  is  rocked  between  its  extreme  positions. 
To  prove  the  correctness  of  the  cam-rod  adjustment,  raise  the  governor 
balls  to  about  the  position  where  they  would  be  when  at  work,  that  is,  to  a 
medium  height,  and  block  them  there.  Then  with  the  connections  made 
between  the  eccentric  and  the  wrist  plate,  turn  the  engine  shaft  slowly  in 
the  direction  which  it  is  to  run,  and  when  the  valve  is  released,  measure 
upon  the  guide  the  distance  that  the  crosshead  has  moved  from  its 
extreme  position.  Continue  to  turn  the  shaft  in  the  same  direction,  and, 
when  the  other  valve  is  released,  measure  the  distance  through  which  the 
crosshead  has  moved  from  the  other  extreme  position.  If  the  cam  rods 
are  properly  set  (cut-off  equalized),  these  two  distances  will  be  equal 
to  each  other.  If  they  are  not,  adjust  the  cam  rods  until  both  valves  are 
released  at  equal  distances  from  the  beginning  of  the  stroke.  The 
governor  should  then  be  blocked  into  its  highest  position  and  the  wrist 
plate  rocked  back  and  forth.  If  the  valves  do  not  pick  up,  the  adjust- 
ment is  satisfactory.  If  they  do  pick  up,  see  how  wide  the  valve  is  opened 
at  the  instant  of  release.  The  valves 
should  not  open  more  than  about  ^ 
in.;  otherwise,  the  engine  might  race 
when  under  no  load. 

8.  SET  THE  SAFETY  TOES  OR  CAMS 
(Z,  Fig.  234).     On  some  engines,  the 
proper  adjustment  of   the   governor 
cam  rods  (H,  Fig.  210)  automatically 
provides  the  adjustment  of  the  safety 
cams.     On  other  engines,  the  safety 
cams  are  adjustable  on  the  knock-off 
lever.     That  is,  the  safety  cam  is  not 
firmly  fixed  by  the  manufacturers  to 
the  collar  which  is  operated  by  the 
cam   rods,    H.     With    either   of    the 
above  constructions,  make  sure  that, 
when  the  governor  block  (S,  Fig.  247) 
is  not  under  the  cross  arm,  the  valves 
are  not  opened  or  picked  up  by  rock- 
ing the  wrist  plate  back  and  forth 

between   its  extreme  positions;  also,  when  the  cross  arm  rests  on  the 
block,  make  sure  that  the  valves  do  pick  up  and  open. 

9.  ADJUST  THE  LENGTH  OF  THE  DASH-POT  RODS  (D,  Fig.  210)  so  that, 
when  the  wrist  plate  is  in  its  extreme  position,  the  valve-arm  toe  (Fig. 
234)  has  equal  clearances  between  the  latch  stops  above  and  below 


Be/t  Crank  In  Hs 
Extreme  Position. 

Upper  Or 

•'L  o  we  ring  Stop 
.-Latch 
'.     Knock-Off 
\  Cam. 


yr* 


z 

Steam-Valve  Arm 
\        ;,     \      ^Dash-Pot  Rod 
|         \       ''Lower  Or  Lifting  Stop 
<o          ^Valve-Arm  Toe 

FIG.  234. — Showing  clearances  which 
should  be  equalized  when  adjusting 
length  of  dash-pot  rod.  (The  clear- 
J,  are  exaggerated  for 


168     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

it,  as  shown  at  G  and  /,  Fig.  234.  The  lower  stop  is  that  catch  on  the 
hook  or  latch  which  raises  the  valve  arm.  The  upper  stop  is  the  upper 
side  of  the  latch  opening  which  brings  the  dash  pot  to  its  lowest  position 
if  the  dash  pot  does  not  of  itself  come  down.  This  adjustment  is  very 
important  because,  if  no  clearance  is  provided  at  J,  the  valve  may  not 
pick  up  and  open;  and,  if  no  clearance  is  provided  at  G,  there  is  danger  of 
breaking  off  the  bonnet  (Fig.  211).  It  is  evident  that  if  there  is  too  little 
clearance  at  G — too  much  clearance  at  J — the  dash-pot  rod  will  hold  up 
the  valve  bell  crank  at  the  steam-valve-rod  end.  Thus,  when  there  is 
too  little  clearance  at  G,  the  bell  crank  cannot  turn  and  must  either  stop 
the  motion  of  the  wrist  plate  or  move  upward  as  a  whole.  If  the  bell 
crank  does  thus  move  upward,  it  imposes  a  force  against  the  bonnet  on 
which  it  is  mounted;  under  such  conditions  the  bonnet  is  usually  broken 
off.  To  safeguard  against  this  damage,  provide  the  equal  clearances  at  G 
and  /  as  directed  above. 

10.  So  ADJUST  THE  DASH-POT  AIR-REGULATING  VALVE  that  the  plun- 
ger will  drop  quickly  enough  that  it  need  not  be  pushed  down  by  the 
latch  hook.     If  the  plunger  descends  too  quickly  and  slams,  the  valve 
should  be  regulated  until  the  proper  speed  is  attained.     The  dash  pot 
should  be  well  lubricated  but  not  excessively.     Too  much  oil  may  choke 
the  air  passages  and  cause  breakage  of  the  dash  pot. 

11.  CHECK  THE  EXHAUST  VALVE  ROD  LENGTH  by  turning  the  engine 
over  in  the  direction  of  running  until  the  crosshead  stands  the  distance 
from  the  end  of  stroke  as  given  under  "trial  compression"  in  Table  193. 
See  then  if  the  marks  E  and  F  (Fig.  233)  are  opposite  each  other.     If  they 
are,  the  engine  will  have  the  compression  recommended  by  that  table. 
If  the  marks  are  not  opposite,  decide  whether  you  want  to  set  the  engine 
for  the  compression  recommended  in  Table  193,  or  instead  if  you  want  to 
try  the  compression  as  the  valves  are  already  set.     If  you  want  the 
recommended  compression,  adjust  the  proper  exhaust-valve  rod   (L, 
Fig.  210)  so  that  marks  E  and  F  (Fig.  233)  are  in  line.     If  you  want  to 
try  the  compression  as  already  set,  simply  turn  the  engine  until  marks  E 
and  F  are  in  line  and  measure  the  distance  of  the  crosshead  from  the 
end  of  the  stroke.     Now  turn  the  engine  to  the  same  distance  from  the 
end  of  stroke  on  the  other  end  and  adjust  the  other  exhaust-valve  rod  so 
the  marks  E  and  F  for  the  other  exhaust  valve  are  in  line.     The  compres- 
sions at  the  two  ends  are  thus  checked  for  equality.     This  entire  step  is, 
however,  very  frequently  omitted  by  many  engineers.     After  this  adjust- 
ment is  finished  the  back  bonnets  or  plates  may  be  replaced  on  the 
cylinder. 

12.  ATTACH  INDICATORS  To  THE  ENGINE  AND  TAKE  DIAGRAMS  at 
both  ends  to  see  that  the  valves  are  properly  set.     This,  of  course, 
is  done  after  the  bonnets  are  replaced  and  the  engine  is  running  under  its 
usual  load.     It  will  usually  be  found  that  slight  imperfections  still  exist  in 
the  valve  action;  see  Sec.  112.     These  may  be  corrected.     Table  194  will 
be  of  great  assistance  in  making  the  fine  adjustments  which  may  now  be 


SEC.  193] 


CORLISS  AND  POPPET  VALVES 


169 


necessary.  In  making  these  adjustments,  one's  attention  should  first  be 
directed  to  the  action  of  the  exhaust  valves.  After  the  exhaust  valves 
function  properly,  the  admission  valves  may  be  adjusted,  if  necessary. 
Very  frequently  a  number  of  rods  must  be  adjusted  to  effect  a  desired 
change.  For  this  reason  setting  the  valves  by  indicator  diagrams  is 
rather  difficult  for  the  inexperienced  engineer;  hence,  the  valves  should 
always  be  set  initially,  as  accurately  as  possible,  by  measurement  as 
hereinbefore  outlined. 


193.  Table  Of  Leads,  Laps,  And  Trial  Compressions  For 
Detaching  Corliss-Valve  Engines. — All  dimensions  are  in 
inches.  Short-stroke  engines  require  slightly  smaller  values. 
Long-stroke  engines  require  larger  values. 


Size  of 
engine 

Steam 
lap* 

Steam 
lead 

Ex- 
haust 
lap 

Trial  i 
com- 
pression 

Size  of 
engine 

Steam 
lap2 

Steam 
lead 

Ex- 
haust 
lap 

Trial1 
com- 
pression 

10  X24 

H 

^4 

Me 

IK 

38  X  52 

Ke 

H* 

Ka 

3 

11  X24 

H 

M4 

Me 

IH 

20  X54 

1^2 

%4 

Ke 

SH 

12  X30 

Ke 

M4 

MB" 

2 

32  X56 

1^2 

H 

Ke 

3^ 

14  X32 

Hi 

Ha 

Me 

2>3 

34  X60 

1^2 

3^ 

Ke 

3^4 

16  X36 

X 

Ha 

Me 

2>3 

36  X66 

H 

H 

K2 

3% 

18  X40 

H 

y32 

Me 

2% 

40  X66 

Ke 

H 

y* 

3% 

20  X42 

H 

H* 

Me 

2« 

42  X  60 

Ke 

%4 

y* 

3^i 

22  X44 

1H2 

Hfs 

Me 

2^ 

44  X  60 

K 

%4 

Ke 

4 

24  X48 

Ke 

Ha 

Me 

2H 

46  X66 

H 

%4 

Ke 

4 

26  X  50 

Ke 

H* 

Me 

2H 

48  X  66 

H 

«4 

Ke 

4 

1  Distance  of  piston  from  end  of  stroke. 

2  These  values  are  for  single-eccentric  engines.     Double-eccentric  engines  are  usually 
set  for  negative  steam  lap  (open  port)  of  one-fourth  the  full  port-opening. 


170     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE      [Div.  5 


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SEC.  194]  CORLISS  AND  POPPET  VALVES 


171 


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172     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

195.  In   Setting   Valves   Of   Double -Eccentric  Detaching- 
Corliss-Valve  Engines  the  same  processes  can  be  used  as 
given  in  Sec.  192  for  single-eccentric  engines  with  the  following 
differences:     The  steam  and  exhaust  valves,  since  they  are 
actuated  from  separate  wrist  plates,  are  set  for  lap  when  their 
respective  wrist  plates  are   central.     The  steam  valves  are, 
however,  set  for  negative  lap;  see  Table  193.     The  rocker 
arms  must  be  set  vertical  when  the  respective  wrist  plates 
are  vertical.     The  exhaust  eccentric  can  be  set  to  give  com- 
pression as  specified  in  Table  193.     The  steam  eccentric  is 
separately  set  to  give  the  desired  lead.     When  setting  the 
steam  eccentric  for  lead,  the  style  of  wrist  plate  which  operates 
the  steam  valves  determines  whether  the  eccentric  should  be 
moved  in  the  same  direction  as  the  crank  or  in  the  opposite 
direction.     Similarly,  an  inspection  of  the  valve  gear  must  be 
made  to  determine  in  which  direction  to  turn  the  eccentric 
when  adjusting  the  exhaust  valves  at  the  point  of  closure  or 
compression.     If  the  exhaust  wrist  plate  is  moved  by  an 
attachment  above  its  point  of  support,  as  with  the  steam 
valves,  the  eccentric  must  be  moved  in  the  direction  in  which 
the  engine  is  to  run,  and  the  position  of  the  exhaust  eccentric 
will  be  nearly  that  of  the  steam  eccentric.     If  the  point  of 
attachment  is  below  the  point  of  support  (Fig.  220) ,  the  eccen- 
tric must  be  moved  in  the  opposite  direction  to  that  in  which 
the  engine  is  to  run. 

196.  Do  Not  Try  To  Lengthen  The  Cut-Off  Of  A  Corliss 
Engine. — Many  engineers  have  lost  employment  for  attempt- 
ing this.     In  order  to  make  an  engine  carry  more  load,  it 
may  seem  necessary  to  adjust  some  rods  to  lengthen  the  cut- 
off (make  it  later).     It  is  true  that  this  will  cause  an  engine 
to  operate  at  a  slightly  higher  speed;  but,  unless  great  care  is 
taken,  one  is  apt  to  make  the  operation  of  the  engine  unsafe 
in  case  the  load  were  suddenly  thrown  off  of  the  engine.     That 
is,  unless  the  upper  governor  collar  is  raised  sufficiently  to  allow 
it  to  rise  and  thus  prevent  the  admission  valves  from  opening, 
there  is  danger,  when  the  load  is  taken  off,  that  the  engine  might 
run  away.     Also,  changing  the  cut-off  by  changing  rod  lengths 
might  prevent  the  safety  cams  from  coming  into  operation,  if 
the  governor  belt  should  break  or  run  off  its  pulley.     Hence : 


SEC.  197]  CORLISS  AND  POPPET  VALVES  173 

197.  To  Make  A  Corliss  Engine  Carry  More  Load  one  of 

only  three  things  should  be  attempted:  (1)  Increase  the  steam 
pressure  if  the  engine  is  safe  for  higher  pressure.  (2)  Reduce 
the  back  pressure.  (3)  Increase  the  engine  speed  as  directed  in 
Div.  6. 

198.  In    Setting  Positively-Operated    Corliss  Valves  And 
Poppet    Valves,    if  manufacturers'   instructions   are  not  at 
hand  or  attainable,  a  greater  deal  is  left  to  the  ingeniousness 
of  the  engineer.     This  must  necessarily  be,  because  of  the 
many  different  forms  of  operating  mechanism  which  these 
valves   employ.     The    instructions   for   several   engines    are 
given  in  following  sections  and  may  be  studied  as  a  guide 
in  so  far  as  the  principles  which  are  given  may  be  readily  applied 
to  different  engines. 

199.  The  Directions  For  Setting  The  Valves  Of  Ball  (Posi- 
tively-Operated) Corliss  Engines,  Fig.  235  (Erie  Ball  Engine 
Co.),  are: 

An  indicator  should  always  be  used  in  setting  the  valves  of  these 
engines,  as  without  its  use  only  a  rough  approximation  can  be  made. 
If  it  is  absolutely  necessary  to  set  them  without  an  indicator,  the  first 
thing  to  do  is  to  put  the  governor  eccentric  in  the  shortest  travel  and 
block  it  there.  This  is  very  important,  as  it  is  impossible  to  set  the 
valves  correctly  without  doing  so.  To  put  the  eccentric  in  its  shortest 
travel,  bring  the  center  of  the  eccentric  in  line  with  the  center  of  the 
suspension  pin  and  the  center  of  the  shaft.  The  governor  should  then  be 
nearly  against  the  stop  which  limits  its  movement  in  that  direction. 

With  the  governor  blocked  in  this  position,  turn  the  engine  until  the 
admission  valve  at  the  crank  end  moves  as  far  toward  opening  as  it  will. 
It  should  not  open  the  port  at  all,  but  should  lack  3^2  to  He  in.  of  coming 
line  and  line.  If  it  does  not,  it  will  be  necessary  to  adjust  the  length  of 
the  reach  rod,  between  the  rocker  arm  and  the  cylinder,  until  the  valve 
lacks  at  least  ^2  in.  of  coming  line  and  line.  Then,  turn  the  engine  to 
head-end  dead  center  and  adjust  the  link  connecting  the  two  gear  cases, 
so  that  the  admission  valve  at  the  head  end  also  lacks  ^2  to  He  in.  of 
opening.  This  will  complete  the  setting  of  the  admission  valves  as  far  as 
it  can  be  done  without  an  indicator.  Upon  taking  cards  it  will  probably 
be  found  that  slight  changes  will  be  advantageous. 

With  regard  to  the  exhaust  valves;  if  the  cylinder  is  less  than  19  in. 
bore,  it  will  have  a  link  connecting  the  cranks  of  the  two  exhaust  valves. 
If  the  cylinder  is  less  than  19  in.  bore,  this  link  should  be  the  same 
length,  center  to  center,  as  the  distance  apart  of  the  two  valve  spindles. 
For  engines  having  19  in.  or  larger  bore  (Fig.  235),  where  the  exhaust 
valves  are  operated  from  a  wrist  plate,  the  short  links  connecting  the 


174     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

valve  cranks  to  the  wrist  plate  should  he  adjusted  to  such  a  length  that, 
when  the  wrist  plate  is  turned  to  bring  the  centers  of  the  two  link  pins 
and  the  center  of  the  wrist-plate  pin  in  a  straight  line,  the  valve  will 
cover  the  exhaust  ports  with  equal  lap  on  each  side  of  the  ports. 

Next,  roll  the  engine  over  by  hand  and  note  whether  one  exhaust  valve 
opens  wider  than  the  other.  If  it  does,  adjust  the  length  of  the  reach 
rod  until  both  valves  open  equal  amounts.  Then  adjust  the  position 
of  the  eccentric  on  the  shaft  so  as  to  have  compression  begin  at  the  desired 
distance  from  the  end  of  the  stroke.  If  an  indicator  is  used,  try  to  adjust 
so  that  the  compression  will  run  up  to  about  one-half  the  throttle  pressure. 


Steam 
Rocker  Arm- 
.-Front  Exhaust 
Bonnet 


'Exhaust-  Valve  Link  Rods  "• 


Rocker-      •   Exhaust  Eccentric  Rod''' 
Arm  • 

Bracket  '' 


E-  Elevation 

FIG.  235. — Plan  and  valve-gear  side  elevation  of  Ball  four-valve  (Corliss)  engine  with 
exhaust  wrist  plate.     (Erie  Ball  Engine  Co.) 

It  is  best  to  have  a  little  more  compression  at  the  head  end  than  at  the 
crank  end,  as  the  piston  travels  faster  at  the  head  end  and  it  requires 
more  compression  there  to  cushion  it  properly.  The  proper  amount  of 
compression  is  the  amount  which  makes  the  engine  run  most  smoothly, 
and  the  only  way  of  determining  it  is  by  experiment  after  the  engine 
is  in  service. 

In  adjusting  the  admission  valves  by  the  indicator,  set  them  so  the 
cards  will  be  practically  alike  at  no  load — slightly  higher  on  the  head 
end  if  anything — and  so  the  initial  pressure  shown  by  the  cards  at  no  load 
will  not  be  over  half  of  the  throttle  pressure.  When  this  is  done  the 
governor  will  automatically  take  care  of  the  other  loads.  At  an  early 


SEC.  200]  CORLISS  AND  POPPET  VALVES  175 

cut-off  there  will  be,  and  should  be,  considerable  wire  drawing.  Do  not 
try  to  prevent  this,  as  it  is  right  to  have  it  that  way,  and  it  is  necessary 
for  the  best  economy. 

200.  The  Directions  For  Setting  Valves  Of  The  Fleming- 
Harrisburg  Four-Valve  Engine  (Harrisburg  Foundry  and 
Machine  Works)  are: 

Disconnect  the  reach  rods  and  locate  the  dead  centers  of  the  engine. 
After  the  centers  have  been  located,  turn  the  engine  until  the  steam-valve 
rocker  arm  stands  plumb.  Now  adjust  the  reach  rods  from  it  to  the  valve 
arms  so  that  the  bell  cranks  are  inclined 
slightly  from  the  vertical  center  line  passing 
through  the  valve  stems,  toward  the  head 
end  as  shown  in  Fig.  236,  where  the  amount 
of  inclination  is  indicated  at  A  and  A\. 
The  amount  of  this  inclination  of  the  steam- 
valve  bell  cranks  varies  for  different  cylinder 
sizes  and  is  as  stated  in  Table  201.  Next, 
turn  the  engine  until  the  exhaust-valve 
rocker  arm  stands  plumb  and  adjust  the 
reach  rods  from  it  to  the  exhaust-valve  FIG.  236.—  Diagram  of  levers 
arms  so  that  these  incline  from  each  other  of  Fleming-Harrisburg  four- 
—  each  to  its  own  end  of  the  cylinder  —  by  valve  engines  (The  dimensions 


the  amount  shown  in  co.umn  B  of  Table  201.  "'  *° 


to, 
For  the  high-pressure  cylinder  of  a  tandem- 

compound  engine  the  exhaust-valve  arms  are  turned  upward  instead  of 
down;  this,  however,  does  not  change  the  angle  of  inclination,  these  arms 
being  set  at  the  inclination  specified  in  the  table,  and  away  from  each 
other  as  before.  For  very  large  low-pressure  cylinders,  where  bell 
cranks  are  used  on  the  exhaust  valves,  these  also  are  set  at  the  inclination 
specified  in  this  table  except  that  they  incline  toward  each  other.  To 
make  the  eccentric  rods  of  proper  length,  adjust  them  so  that  the  rocker 
arms  will  travel  equally  on  both  sides  of  their  neutral  vertical  positions. 
The  valves  should  next  be  set  in  the  proper  relation  to  the  valve  arms 
before  clamping  the  arms  to  the  stems,  and  forcing  the  set  screws  into 
place.  To  do  this,  place  the  engine  on  its  head-end  dead  center  and 
disconnect  the  springs  from  the  governor.  If  the  governor  has  been 
adjusted  for  proper  engine  speed  measure  the  length  of  each  spring  before 
disconnecting  it  so  that,  when  the  springs  are  replaced,  the  initial  tension 
can  be  restored.  With  the  springs  removed,  block  the  governor  in  the 
position  of  least  travel,  that  is,  against  the  outer  stops;  remove  the  valve 
cover-plates  and  note  the  marking  of  the  valves  and  ports  (Figs.  237  and 
238).  This  marking  will  be  found  on  the  ends  of  the  valves  and  at  the 
ends  of  the  cylinder  ports,  the  steam  edges  and  exhaust  edges  all  being 
marked  S. 


176     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Dw.  5 


Now,  on  simple  engines  and  on  the  high-pressure  cylinders  of  compound 
engines,  set  the  head-end  steam  valves  so  as  to  overlap  the  port  edges,  S, 
by  about  He  in.,  which  may  be  termed  negative  lead.  Then  clamp  this 

I        ,  Steam  Supply 
\-    ii         Flancie 


Steam 
Chest 


Flange''         \ 
FIG.  237. — Exterior  outline  of  Harrisburg  four-valve  engine. 

valve  arm  on  the  stem  and  turn  the  engine  in  the  direction  in  which  it 
will  run  to  the  crank-end  center.  Set  the  crank-end  steam  valve  with 
about  ^2  in.  lap  or  negative  lead  and  clamp  the  valve  arm  on  the  stem. 


To  Open 


FIG.  238. — Vertical   section    through    cylinder   and   valves    of   Harrisburg   four-valve 

engine. 

This  negative  lead  is  especially  necessary  for  condensing  engines,  to  prevent 
the  engine  from  running  away  when  the  load  is  thrown  off.  The  ports 
usually  do  not  open  to  steam  at  all  with  the  governor  blocked  in  this 


SEC.  200]  CORLISS  AND  POPPET  VALVES  177 

position,  and  positively  must  not  open  more  than  enough  to  admit 
sufficient  steam  to  overcome  the  friction  of  the  engine. 

The  blocking  of  the  governor  should  now  be  changed.  Fix  it  in  such 
a  position  as  will  give  about  H  cut-off.  To  do  this,  the  point  of  cut-off 
should  be  located  on  the  guides  by  making  marks  on  the  lower  guide  in 
line  with  the  mark  on  the  crosshead  shoe  for  each  dead-center  position, 
and  dividing  the  distance  between  them  into  three  equal  parts.  Now 
turn  the  engine  over  until  the  mark  on  the  crosshead  shoe  is  in  line 
with  the  point  on  the  guide  corresponding  to  H  cut-off  for  the  head  end 
and  block  the  governor  so  that  the  valve  is  line  and  line  at  the  steam 
edge.  Next,  turn  the  engine  over  until  the  valve  shows  the  cut-off  on  the 
crank  end.  It  will  be  noted  that  the  crosshead  has  not  traveled  the  full 
Yz  stroke,  as  indicated  by  the  crosshead  and  guide  marks,  by  from  % 
to  1  in.,  depending  on  the  size  of  the  engine.  An  adjustment  of  the  valves 
can  be  made,  which  will  lessen  this  amount,  but  it  will  increase  the  differ- 
ence in  lead  between  the  two  ends.  Hence,  this  adjustment  must  be 
made  to  the  best  advantage,  lead  and  cut-off  considered.  It  will  be 
noted  that  lead  materially  increases  for  later  points  of  cut-off  and  tends 
to  make  the  engine  pound  if  too  great. 

The  exhaust  valves  may  be  properly  set  by  turning  the  engine  over  to 
bring  the  valve  arms  and  rocker  arms  into  their  neutral  positions.  With 
the  engine  in  this  neutral  position,  adjust  the  head-end  exhaust  valve  with 
about  y\  G  in.  lap  and  the  crank-end  exhaust  valve  with  Y±  in.  lap.  Now, 
for  determining  trial  compression  make  a  mark  on  the  guides  measuring 
from  each  dead-center  mark:  For  the  high-pressure  cylinder  of  a  com- 
pound engine  the  mark  should  be  about  1^  in-  from  each  end  of  the  stroke. 
For  a  simple  engine  or  the  low-pressure  cylinder  of  a  compound  engine 
the  mark  should  be  about  3  in.  from  the  end  of  the  stroke.  These 
measurements  will  increase  for  engines  having  24  in.  or  larger  stroke. 
Now  clamp  the  two  exhaust  valves  on  the  valve  stems,  and  turn  the 
engine  over  in  the  direction  in  which  it  will  run  until  the  crosshead  mark 
coincides  with  the  head-end  mark  just  made  on  the  guides.  This  will 
bring  the  crank  pin  below  the  center  line  of  the  engine,  and  the  piston  in 
position  for  compression  at  the  head  end  of  the  cylinder.  With  the 
crosshead  still  in  this  position,  turn  the  eccentric  around  on  the  shaft  until 
the  valve  and  port  edges  (S,  Fig.  237)  coincide  for  the  head-end  valve. 
This  valve  is  now  in  proper  relation  to  the  crank  for  compression  and  the 
eccentric  set  screw  should  be  set  down  on  the  shaft.  The  engine  should 
now  be  turned  over  until  the  crosshead  mark  coincides  with  the  crank- 
end  compression  mark  on  the  guide,  when  the  two  edges  S  of  the  crank- 
end  exhaust  valve  and  seat  should  coincide.  If  they  do  not,  loosen  the 
valve  stem  in  the  arm  and  turn  the  valve  so  that  these  two  marks  do 
coincide  and  fasten  it  again.  This  valve  is  also  now  right  for  compres- 
sion. With  the  setting  just  described,  the  crank-end  exhaust  port  should 
be  about  one-half  open  when  the  engine  is  on  head-end  dead  center. 
This  should  also  be  true  for  the  head-end  valve  when  the  engine  is  turned 
on  the  crank-end  center. 

12 


178    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 


In  valve  setting,  always  (Sec.  153)  turn  the  engine  over  in  the  direction 
it  runs,  never  turning  it  past  a  desired  point  and  then  back  to  it,  as  the 
lost  motion  will  prevent  accurate  adjustment.  When  turning  an  engine 
over  on  which  the  rods  have  not  been  adjusted,  care  should  be  taken  to 
insure  against  jamming  of  the  valve  gear;  that  is,  forcing  it  beyond  its 
normal  travel  in  one  direction  and  straining  it,  due  to  the  rods  being  too 
long  or  too  short. 

201.  Table  Showing  Advance  Of  Steam  And  Exhaust 
Valve  Arms  On  Harrisburg  Four-Valve  Engines. — Dimensions 
are  all  in  inches  and  refer  to  Fig.  236. 


Cylinder 

Advance  steam  valve  bell  cranks 

Advance   ex- 
haust valve  arm, 

sizes 

A 

A, 

B 

9    -10^ 

KG 

Ke 

0 

11     -14>£ 

H* 

% 

0 

15     -17 

IH 

H 

0 

1714-20 

H 

% 

K 

19M-S4^ 

IK 

H 

H 

25     -29 

iH 

i 

y8 

30    -343^ 

IH 

i 

7/8 

35     -40^ 

IH 

IH 

IH 

46     -56 

m 

IH 

iK 

202.  Directions  For  Setting  Valves  Of  Ridgway  Four-Valve 
Engines. — All  engines  are  set  in  the  shop  to  dimensions  shown 
in  Table  203  which  apply  to  Figs.  239  and  240.  They  are  then 
set  by  indicator  and  reference  marks  are  made  on  all  eccentric 
and  valve  rods.  These  marks  are  3  in.  apart  on  small  engines 
and  4  in.  apart  on  large  engines.  All  arms  are  marked  with  a 
chisel  so  that  if  at  any  time  they  have  moved  it  will  be  possible 
to  return  them  to  their  original  location.  To  set  the  valves: 
Use  the  marks  if  possible.  If  marks  are  not  visible,  set  to  the 
dimensions  of  Table  203.  Then  use  an  indicator  to  perfect 
the  setting;  see  Sec.  112  and  Sec.  175.  Table  204  shows  the 
results  of  adjustments  to  the  simple  and  cross  compound 
engines.  Table  205  shows  the  results  of  adjustments  to  the 
four-valve  tandem  compound  engines. 


SEC.  203] 


CORLISS  AND  POPPET  VALVES 


179 


203.  Table  Of  Dimensions  For  Setting 
Ridgway  Simple  Four-Valve  Engines.— 
The  steam  valves  are  set  with  the  gov- 
ernor bar  blocked  against  the  outer  stop, 
thus:  When  crank  is  on  head-end  dead 
center,  set  head-end  valve  with  J^2  m- 
lead.  When  crank  is  on  crank-end  dead 
center,  set  crank-end  valve  with  Jf  6  in- 
lead.  Set  exhaust  valves  and  eccentric  to 

.  .  FIG.     239.  — Showing 

the  following  dimensions  which  apply  to   method  of  locating  ex- 
Figs.   239   and  240.  haust  eccentric  on  shaft 

of  Ridgway  engine. 


Head-End 
Steam  Valve             Crank-End  Steam  Valve 

t     I  A                       ll_) 

^•Center  Linf 
Of  Gear  Box 

C 

—  r^ 

Valves  Move  To  Open 


To  Eccentrics- 


Crank-End  Exhaust 
Valve 

FIG.  240. — Diagram  of  valve  gearing  of  Ridgway  simple  four-valve  engine. 


Compression 

Length  between  centers  of  valve  rods 

T          f  ' 

of  ex- 

Bed 

Stroke 

Head 

Crank 

Steam  valve  rods 

Exhaust  valve  rods 

haust 

eccentric 

on  shaft 

C 

£) 

X 

L 

D 

12-14 

w 

4" 

2'-10K" 

2'-5H" 

2'-  9^" 

17^" 

2" 

F 

14-16 

5" 

W 

3'-  2K" 

2'-  6^^ 

3'-  W 

\*w 

2«" 

H 

16-18 

5H" 

5" 

3'-  7H" 

2'-  9>i/' 

3'-  6^' 

19%" 

3" 

J 

18-20 

BH" 

6" 

3'-ll^" 

2'-H^" 

3'-llH' 

22" 

3J^' 

K 

22-24 

7" 

6H' 

4'-  3^" 

2'-H^". 

4'-.  3>i' 

22" 

3>i' 

L 

20-22-24 

7«" 

7" 

4'-  8H" 

3'-  5^"' 

4'-  7^' 

2'-2H" 

3^' 

M 

26-28 

8" 

7M" 

5'-  0^" 

3'-  5^» 

4'-ll%' 

2'-2K" 

3^' 

N 

24-26-28 

m" 

8" 

5'-  5^" 

4'-0" 

5'-  4" 

2'-5K" 

4H' 

0 

30-32 

9" 

w 

5'-  9H" 

4'-0" 

5'-  8" 

2'-5M" 

4M' 

P 

28-30-32 

W 

9" 

Q 

34-36 

10" 

9K" 

204.  Table    Of    Results    Of    Adjustments    To    Ridgway 
Simple    And    Cross    Compound    Four-Valve    Engines. — The 

letters  referred  to  are  shown  on  Fig.  240. 


180    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 


Steam  valves 


Adjustment 

Head  end 

Crank  end 

Admission 

Cut-off 

Admission 

Cut-off 

Turn  stem  A  in  arm  B  counter- 
clockwise or  shorten  rod  C. 

Earlier     or 
more  lead 

Later 

Unchanged 

Unchanged 

Turn  stem  E  in  arm  F  clockwise 
or  lengthen  rod  D. 

Unchanged     Unchanged 

Earlier     or 
more  lead 

Later 

Lengthen  reach  rod  M  or  turn 
shaft  O  in  arm  P  counter- 
clockwise. 

Earlier     or 
more  lead 

Later 

Later   or 
less  lead 

Earlier 

Exhaust  valves 


Adjustment 

Head  end 

Crank  end 

Release 

Compres- 
sion 

Release 

Compres- 
sion 

Turn  stem  G  in  arm  H  clockwise 
or  shorten  rod  K. 

Earlier 

Later 

Unchanged 

Unchanged 

Turn  stem  L  in  arm  J  clockwise  or 
shorten  rod  L. 

Unchanged 

Unchanged 

Earlier 

Later 

Shorten  reach  rod  N  

Earlier 

Later 

Later 

Earlier 
Earlier 

Turn    exhaust    eccentric    around 
shaft  in  direction  of  rotation  .... 

Earlier 

Earlier 

Earlier 

H.R  Cylinder 

Head- End  Steam  Valve  Crank-End  Steam  \b/ve 


L.  P.  Cylinder 

Head-End  Steam  Valve  Crank- End  Steam  Valve 

I 


ToL.P  Eccentric 


Head-End  Exhaust 
Valve 


Valve 


Head- End  Exhaust  Crank- End  Exhaust 

Valve  Valve 


FIG.  241. — Diagram  of  valve  gearing  of  Ridgway  tandem-compound  four-valve  engine. 


SEC.  205  J 


CORLISS  AND  POPPET  VALVES 


181 


205.  Table  Of  Results  Of  Adjustments  To  Ridgway  Tandem 
Compound  Four -Valve  Engines. — The  letters  referred  to  are 
shown  on  Fig.  241. 

High-pressure  steam  valves 


Adjustment 

Head  end 

Crank  end 

Admission 

Cut-off 

Admission 

Cut-off 

Turn  stem  A  in  arm  B  counter- 
clockwise or  shorten  rod  C. 

Earlier     or 
more  lead 

Later 

Unchanged 

Unchanged 

Turn  stem  E  in  arm  F  clockwise  or 
shorten  rod  D. 

Unchanged 

Unchanged 

Earlier     or 
more  lead 

Later 

Lengthen  reach  rod  M  or  turn 
shaft  O  in  arm  P  counterclock- 
wise. 

Earlier     or 
more  lead 

Later 

Later    or 
less  lead 

Earlier 

Low-pressure  steam  valves 


Adjustment 

Head  end 

Crank  end 

Admission 

Cut-off 

Admission 

Cut-off 

Turn  stem  A  in  arm  B  counter- 
clockwise or  shorten  rod  C. 

Earlier     or 
more  lead 

Later 

Unchanged 

Unchanged 

Turn  stem  E  in  arm  F  clockwise  or 
shorten  rod  Z>. 

Unchanged 

Unchanged 

Earlier     or 
more  lead 

Later 

Lengthen  reach  rod  N  or  turn 
shaft  Q  in  arm  R  counterclock- 
wise. 

Earlier     or 
more  lead 

Later 

Later   or 
less  lead 

Earlier 

Turn  low-pressure  eccentric 
around  shaft  in  direction  of 
rotation. 

Earlier     or 
more  lead 

Earlier 

Earlier     or 
more  lead 

Earlier 

182    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

High-pressure  exhaust  valves 


Adjustment 

Head  end 

Crank  end 

Release 

Compres- 
sion 

Release 

Compres- 
sion 

Turn  stem  G  in  arm"  H  clockwise 
or  shorten  rod  K. 

Earlier 

Later 

Unchanged 

Unchanged 

Turn  stem  L  in  arm  J  counter- 
clockwise or  lengthen  rod  L. 

Unchanged 

Unchanged 

Earlier 

Later 

Shorten  reach  rod  N  . 

Earlier 

Later 

Later 

Earlier 

Turn  low-  pressure  eccentric 
around  shaft  in  direction  of 
rotation. 

Earlier 

Earlier 

Earlier 

Earlier 

Low-pressure  exhaust  valves 


Adjustment 

Head  end 

Crank  end 

Release 

Compres- 
sion 

Release 

Compres- 
sion 

Turn  stem  G  in  arm  H  clockwise 
or  shorten  rod  K. 

Earlier 

Later 

Unchanged 

Unchanged 

Turn  stem  L  in  arm  J  counter- 
clockwise or  shorten  rod  S. 

Unchanged 

Unchanged 

Earlier 

Later 

Shorten  reach  rod  N. 

Earlier 

Later 

Later 

Earlier 

Turn  low-pressure  eccentric 
around  shaft  in  direction  of 
rotation. 

Earlier 

Earlier 

Earlier 

Earlier 

206.  The  Directions  For  Setting  Poppet  Valves  On  Ames 
"Una -flow"  Engines  (Ames  Iron  Works)  are:  The  valve 
gear  should  be  assembled  and  set  according  to  the  tram  marks, 
M,  found  on  the  rods  and  rod  heads  as  shown  in  Fig.  225. 
The  proper  distance,  in  inches,  between  punch  marks  on  the 
rod  and  head  will  be  found  stamped  on  the  rod.  If,  for  any 
reason,  the  marks  cannot  be  found,  a  preliminary  setting  of 


SEC.  206] 


CORLISS  AND  POPPET  VALVES 


183 


the  valves  can  be  made  as  follows  and  the  final  setting  made 
after  an  indicator  has  been  used  on  the  engine.  (See  Fig.  245 
for  illustration  of  complete  engine.) 


Spring-Tension 
j_  Screw 
'^Bonnet  Cap , 


1.  Two- VALVE  TYPE,  straight  una-flow.  (a)  MAIN  VALVES. 
Connect  the  eccentric  rod  to  the  rocker  arm  and  adjust  the  length  of  the 
rod  so  that  the  rocker  travels  equal  distances  to  both  sides  of  the  vertical 
when  the  engine  is  turned  over  by  hand.  Then  adjust  the  valve  stems 
(F,  Fig.  242)  so  that  there  will  be  about  Kooo  in.  space  between  the 
flat  part  of  the  cams  and  the  rollers  in  the  roller  rods.  This  space  can  be 
measured  with  a  thickness  gage  in- 
serted through  the  peephole  opening  in 
the  side  of  the  bonnet.  This  space 
will  increase  after  the  engine  has  been 
warmed  by  the  high-temperature 
steam  and  should  be  about  "Kooo  m- 
when  the  engine  is  in  normal  opera- 
tion. Next,  connect  the  reach  rod,  R 
(Fig.  225),  to  the  crank-end  roller 
rod,  C,  and  adjust  the  length  of  the 
reach  rod  so  that,  with  the  engine  on 
crank-end  dead  center,  the  roller,  Q 
(Fig.  242)  in  the  crank-end  roller  rod 
just  touches  the  cam,  M.  Then, 
with  the  engine  on  head-end  dead 


'Adjust  Clearance  Here 

FIG.  242. — Section  through  bonnet  and 
valve  of  Ames  uniflow  engine. 


center,  adjust  the  ball  rods,  B,  over  the  cylinder,  so  that  the  roller  in  the 
head-end  roller  rod  just  touches  the  cam  as  at  the  crank  end. 

With  the  engine  running  under  normal  load,  take  indicator  diagrams 
and  then  make  whatever  adjustments  seem  necessary  to  make  the  diagram 
as  desired.  In  making  these  adjustments,  give  attention  first  to  the 
crank-end  valve.  Then,  after  that  is  properly  adjusted,  set  the  head-end 
valve.  The  effects  of  adjustments  of  the  reach  and  ball  rods  are  given  in 
Table  207.  Bear  in  mind  that  the  valve  motion  is  very  sensitive  to 
adjustment  and  that  very  little  change  in  rod  length  is  required  to  make  a 
very  material  change  in  the  indicator  diagrams.  In  most  cases,  the  lead 
will  show  later  and  the  admission  line  will  not  be  as  good  at  the  head  end 
as  at  the  crank  end,  and  if  there  is  any  difference  in  the  compression  it 
will  show  highest  at  the  head  end. 

Care  should  be  exercised  when  increasing  the  lead  on  the  valves,  while 
the  engine  is  carrying  load,  not  to  increase  it  to  such  an  extent  that 
the  governor  will  lose  control  of  the  engine's  speed  when  operating  at 
friction  load  or  no  load.  This  condition  may  occur  if  the  rollers  are 
adjusted  so  far  under  the  cams  with  the  engine  carrying  a  load  that,  when 
the  load  is  thrown  off  and  the  governor  is  on  its  minimum  travel,  the  rollers 
may  still  be  contacting  with  the  cams  and  lifting  the  valves  slightly. 
Steam  would  thus  be  admitted  to  the  cylinder  causing  the  governor  to 


184    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

lose  control  of  the  engine  at  friction  or  light  load.  If  this  occurs  it  is  only 
necessary  to  decrease  the  lead  to  such  an  extent  that,  with  the  maximum 
steam  pressure,  the  governor  will  control  the  engine  at  friction  load. 
Typical  indicator  diagrams  are  shown  in  Fig.  243.-/. 

If  the  engine  is  to  operate  sometimes  condensing  and  sometimes  non- 
condensing,  the  valves  should  be  set  for  condensing  operation,  as  a  con- 
densing engine  will  not  operate  satisfactorily  with  as  much  lead  when 


I- Indicator  Diagrams 
From  Una-Flow  Engine 
Non-Condensing 


[-  Indicator  Diagrams  From 
Control  led-Compression  Una-Flow 
All  Diagrams  Taken 
Non-Condensing 


Diagram  Shows  Late  Admission 
On  The  Head-End 


Diagram  ShowslateAdmiss 
On  The  Crank- End 


Diagram  Shows  Late  Admission 
On  The  Crank- End 


Correct  Non- Condensing 
Diagram 


Diagram  Shows  Crank-End 
Exhaust  Valve  Closes  Too 
Early  Causing  High 
Compression  On  Crank-End 


Correct  Condensing  Diagram 


Diagram  Shows  Head-End 
Exhaust  Valve  Closes  Too 
Early  Causing  High 
Compression  On  Head-End 


A  Correct  Diagram 
FIG.  243. — Typical  indicator  diagrams  from  Ames  "una-flow"  engines. 


operating  condensing  as  it  will  when  operating  non-condensing,  due 
to  the  action  of  the  vacuum  in  addition  to  the  very  early  admission  of 
steam. 

(6)  AUTOMATIC  BY-PASS  VALVES  (Fig.  244).  All  engines  built  for 
condensing  operation  are  furnished  with  by-pass  valves  which  are  auto- 
matically controlled  by  the  pressure  in  the  exhaust  pipe  or  exhaust  belt 
of  the  engine.  The  object  of  the  by-pass  valves  is  to  automatically 
increase  the  volumetric  clearance  of  the  engine  in  case  of  loss  of  vacuum 
or  in  case  the  vacuum  falls  below  a  predetermined  point,  also  to  auto- 
matically decrease  the  clearance  when  the  vacuum  is  restored  or  raised 


SEC.  206] 


CORLISS  AND  POPPET  VALVES 


185 


above  the  predetermined  point.  The  additional  clearance  space  is 
within  the  cylinder  head  at  the  bottom.  The  by-pass  valve  opens  or 
closes  communication  between  the  cylinder  and  this  additional  clearance 
volume.  The  valve  of  Fig.  244  does  not  operate  with  each  stroke  of  the 
engine  but  only  when  the  vacuum  changes  through  the  predetermined 
point. 

The  vacuum  acts  upon  a  piston,  P  (Fig.  244),  which  is  within  a  cylinder, 
C,  and  thus  allows  the  atmospheric  pressure  from  above  to  force  the  piston 
downward  against  a  spring,  thus  drawing  down  the  valve  and  closing  it. 
If  the  vacuum  falls  below  the  predetermined  point,  the  spring  forces  the 
piston  upward  and  opens  the  valve.  By  adjusting  the  tension  on  the 
spring,  the  valve  can  be  made  to  operate  at  any  desired  point  within 


By-Pass  Valve 


This 

Hole  Is  For  l/enf..  .-' 
Ana 'Should 'y'' 
Be  Left  Open 
To  Atmosphere 


Pi  pels  Connected 
To  Central  Exhaust 
Be'*  Washer- 

Screw  For  Adjusting  t 
Tension  On  Spring'' 


-By-Pass --Valve  Cage 

•By-Fbss-Va/ve  Piston 
I -By- Pass-Valve  Cylinder 

C 

"Spring  Forces  Valve 
From  Seat  When  Vacuum 
Falls  Be/ow  a  Predeter- 
mined Point 
•When  Vacuum  On  Piston 
Overcomes  Tension  On 
Spring  The  Valve  Closes 


FIG.  244. — Section  through  automatic  by-pass  valve  of  Ames  "una-flow"  engine. 


reasonable  limits.  When  operating  at  a  vacuum  of  24  to  26  in.  of  mer- 
cury, the  spring  should  be  adjusted  to  operate  at  15  to  18  in.  vacuum. 
These  valves  should  be  removed  at  least  once  every  six  months  and 
examined  to  insure  that  they  are  not  gummed  or  corroded. 

2.  FOUR- VALVE  TYPE,  controlled-compression  una-flow.  The  steam 
valves  are  set  exactly  as  on  the  two-valve  type.  If  no  marks  are  avail- 
able for  setting  the  eccentric,  it  should  be  so  located  that  the  center  line  of 
the  keyway  is,  in  rotation,  52  to  53  degrees  back  of  the  crank  pin,  except 
on  34  to  36-in.  stroke  engines,  for  which  engines  the  center  line  of  the 
keyway  should  lead  the  crank  pin  in  rotation  by  approximately  127  to 
128  degrees.  Then  adjust  the  eccentric  rod,  E  (Fig.  245),  so  that  the 
exhaust  rocker  arm,  R,  will  travel  equal  distances  to  both  sides  of  the 
vertical. 


186    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

Remove  the  covers  on  the  opposite  side  of  the  cage  from  the  rocker 
lever.  This  will  allow  full  view  of  the  cams,  Q  (Fig.  225).  The  roller  in 
the  small  crosshead  on  the  exhaust  valve  stem  should  be  adjusted, 
through  the  small  rectangular  opening  on  the  side  of  the  cage,  so  that 
there  will  be  about  Mooo  in.  space  between  the  cam  and  roller,  at  a  point 
on  the  round  part  of  the  cam  just  before  the  lifting  part  comes  into  con- 
tact with  the  roller.  The  smaller  this  space  is  kept,  the  more  quiet  will  be 
the  operation  of  the  valves;  but,  to  insure  proper  closing  of  the  valves, 
some  clearance  must  be  provided. 

Turn  the  engine  over  in  direction  of  rotation  until  it  is  on  dead  center 
(Sec.  153)  and  make  a  mark  on  the  side  of  the  crosshead  shoe  and  a  similar 
mark  on  the  crosshead  guide  directly  in  line  with  the  one  on  the  crosshead 
shoe.  Turn  the  engine  to  the  other  dead  center  and  mark  the  guide  at 
that  end  in  the  same  way.  This  will  provide  for  conveniently  measuring 


•  Oil  Supply  Tank  And  Filter      ,Va/ve  Cages* 
,-Steam-va/ve  »    /       Throttle 

^     Reach  Rod  .  _JH*L      :  Valve 


Sub-base-'' 


Exhaust  Rocker-arm  'Exhaust-  valve  Cages' 


FIG.  245. — Governor  and  valve-gear  side  of  Ames  "controlled  compression  una-flow" 
engine.     (Ames  Iron  Works.) 


the  distance  the  piston  may  be  from  the  end  of  its  stroke.  Turn  the 
engine  over  until  the  piston  is  1  in.  from  head-end  center  and  the  crank  pin 
below  the  engine's  center  line.  In  this  position  adjust  the  exhaust  reach 
rod,  (Fig.  245)  Q,  so  that  the  cam  in  the  crank-end  cage  is  just  touching 
the  roller.  Turn  the  engine  to  within  1  in.  of  crank-end  dead  center  and 
adjust  the  exhaust  valve  rod,  V,  so  that  the  cam  in  the  head-end  cage  is 
barely  touching  its  roller. 

Further  adjustments  may  be  made,  after  the  engine  is  running,  from 
the  indicator  diagrams.  In  making  adjustments  on  the  reach  rod  and 
valve  rod,  it  should  be  remembered  that  the  exhaust  valves  open  as  their 
small  levers  move  toward  the  ends  of  the  cylinder — except  on  34-in.  and 
36-in.  stroke  engines  where  they  open  when  the  levers  move  toward  the 
center  of  the  cylinder.  The  effects  of  adjustments  are  given  in  Table  207 
and  typical  indicator  diagrams  are  shown  in  Fig.  243.-/7. 


SEC.  207] 


CORLISS  AND  POPPET  VALVES 


187 


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188     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

208.  In  Setting  The  Valves  Of  A  Chuse  Condensing  Uniflow 
Engine,  Figs.  227  and  391,  proceed  as  follows  (Chuse  Engine 
and  Manufacturing  Company) : 

First  loosen  the  lock-ring  nut  on  the  ball-and-socket  joint  on  the 
crank-end  roller  slide.  This  will  permit  dropping  down  the  reach  rod 
which  extends  from  the  rocker  arm  to  the  roller  slide,  so  that  the  slides 
can  be  moved  back  and  forth  by  hand.  Next,  remove  the  covers  or  caps 
from  the  camheads.  This  will  uncover  the  upper  ends  of  the  cam  cross- 
heads,  to  which  the  cams  are  fastened.  It  will  also  uncover  the  upper 
side  of  the  slides,  in  which  the  rollers  are  located.  Then  push  one  of  the 
slides  just  far  enough  so  that  the  roller  will  be  under  the  thin  end  of 
the  cam.  Observe  carefully  that  the  proper  clearance  exists  between  the 
roller  and  the  cam  at  this  point  by  introducing  between  them  a  piece  of  an 
indicator  card  or  a  Kooo-in.  thickness  gage.  If  the  cam  is  too  low,  so 
that  a  paper  will  not  enter,  raise  the  cam  crosshead  by  loosening  the 
locknut  on  the  valve  stem  at  the  lower  end  of  the  cam  crosshead  and 
then  screwing  out  the  valve  stem  slightly — just  enough  to  provide  the 
necessary  clearance  between  the  cam  and  the  roller. 

Then  tighten  the  locknut  and  again  try  the  clearance.  Too  much 
space  between  the  cam  and  the  roller  will  cause  the  roller  to  strike  too 
hard  against  the  incline  of  the  cam,  thereby  producing  noisy  running. 
It  is  also  well  to  lift  up  the  cam  crosshead  and  valve  and  release  them  to 
insure  that  the  valve  is  solidly  on  its  seat.  After  adjusting  both  crank- 
end  and  head-end  valves  in  this  manner,  the  cam  heads  should  be  replaced. 
Be  sure  that  the  springs  are  in  their  proper  positions  before  tightening 
down  the  cap  screws  on  these  covers.  Then  connect  the  reach  rod  to 
the  roller  slide  again  and  place  the  engine  on  the  exact  crank-end  dead 
center. 

With  the  engine  on  crank-end  dead  center,  lengthen  or  shorten  the 
reach  rod  until  the  roller  lifts  the  crank-end  valve  ^2  in.  This  lift  can 
best  be  measured  with  a  small  inside  caliper  by  setting  it  to  the  distance 
between  the  upper  end  of  the  stem  sleeve  and  the  under  side  of  the 
locknut  on  the  valve  stem.  After  the  crank-end  valve  has  been  set  in 
this  manner,  turn  the  engine  over  to  the  exact  head-end  dead  center. 
Increase  or  decrease  the  distance  between  the  slides,  by  lengthening  or 
shortening  the  rod  which  connects  the  two  slides,  until  the  head-end 
valve  is  lifted  just  ^62  in.,  as  was  the  crank-end  valve  before.  This 
completes  the  valve  setting  so  far  as  it  can  be  done  by  measurement. 
The  final  setting  is  made  after  taking  indicator  diagrams;  see  Sec.  112.^ 

209.  The    Directions    For    Setting    Valves    Of  "Lentz" 
Poppet-Valve    Engines    (Erie  City  Iron  Works)   are:     The 
setting  of  all  valves  except  those  which  are  controlled  by  the 
governor  is  left  to  the  operating  engineer,  insofar  as  there  are 
no  rigid  rules  laid  down  by  the  manufacturers.     An  approxi- 


SEC.  2101 


CORLISS  AND  POPPET   VALVES 


189 


mate  setting  can  be  made  by  measurement  as  directed  below 
—the  final  setting  can  then  be  made  from  indicator  diagrams. 
See  Fig.  383  for  illustration  of  complete  engine. 

1.  STEAM  VALVES.  The  steam  valves  which  are  under  the  governor's 
control  have  their  eccentric  driving  block  (D,  Fig.  246)  keyed  to  the 
lay-shaft,  L.  The  correct  setting  can  be  checked  as  follows:  Turn  the 
lay-shaft  until  the  eccentric  rod  stands  at  right  angles  to  the  driving 
block,  D,  as  shown  in  Fig.  246.  If  the  governor  is  now  opened  and  closed 
from  minimum  to  maximum  position,  the  cam  lever  should  show  a 
hardly  perceptible  motion.  This  is  the  correct  position  for  the  lead, 
and  the  valve  spindle  must  be  so  adjusted  that  the  roller  just  touches 
the  curve  of  the  cam  and  that  with  the  least  motion  of  the  side  shaft,  the 


.-Roller  Guide 
'     .-Steam- Cam 
:'     Lever 


Exhaust  Eccentric 


Steam  Eccentric '' 


Governor 
Ring  • 


I'Eleva-tion 

Lay  Shaft 


:-Plan 


--Steam 

Eccentric 

Strap 


FIG.  246. — High-pressure  steam-valve  gear  of  "Lentz"  engine.     (Erie  City  Iron  Works.) 

valve  lift  commences.  In  case  the  steam  valves  ever  have  to  be  taken 
out,  the  correct  position  in  which  to  replace  them  may  be  determined 
as  follows:  It  will  be  noticed  that  there  is  a  small  center-punch  mark  in 
the  valve  stem,  S,  and  one  in  the  roller  guide,  R.  When,  at  the  factory, 
the  valve  is  properly  located,  these  marks  are  exactly  2  in.  apart.  To 
replace  the  valve  it  is  only  necessary  to  set  a  pair  of  dividers  to  2  in.  and 
adjust  the  length  of  the  valve  spindle  until  these  marks  are  just  2  in.  apart. 
If  the  engine  has  been  in  operation*  several  years,  this  dimension  may  be 
slightly  different  on  account  of  natural  wear  on  the  roller  and  cam.  The 
final  position  may  then  be  determined  by  turning  the  valve  stem  a  minute 
fraction  of  a  turn  until  a  position  is  found  where  the  cam  will  engage 
the  roller  with  an  easy  and  smooth  effect  without  jar  and  noise.  All 
other  eccentrics  being  clamped  to  the  shaft,  they  can  be  easily 
turned  in  any  direction.  By  turning  the  low-pressure  steam  eccentric 
forward,  the  lead  is  increased  and  cut-off  made  later;  and  vice  versa  when 
turning  in  the  opposite  direction.  By  "forward"  is  meant  in  the  direc- 
tion of  rotation  of  the  side  shaft,  and  by  backward,  against  the  rotation 


100    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  5 

of  the  side  shaft.  When  shortening  the  eccentric  rods  on  the  steam 
valves,  lead  is  increased  and  cut-off  made  later,  and  vice  versa  when 
lengthened. 

2.  EXHAUST  VALVES.     When  turning  the  exhaust  eccentric  forward, 
release  and  compression  are  made  earlier,  and  vice  versa  when  turned 
backward. 

3.  VALVE  SPRINGS.     Valve  springs  should  be  so  adjusted  as  to  keep 
the  roller  and  cam  in  contact  without  throwing  unneessary  load  on  the 
valve  gear. 

210.  The  Directions  For  Setting  Valves  Of  Vilter  Poppet- 
Valve  Engines  (Fig  226)  are :  Since,  on  these  engines,  the  valve- 
operating  mechanism  comprises  the  same  essential  parts  as 
does  that  of  a  double-eccentric  Corliss-valve  engine  the  setting 
of  the  valves  is  almost  the  same  as  given  in  Sec.  195  for  the 
latter.  In  the  following  directions  only  those  adjustments 
which  differ  essentially  from  the  setting  of  Corliss  valves  are 
treated  in  detail. 

ADJUST  THE  ECCENTRIC  RODS  AND  REACH  RODS,  as  for  a  double  eccen- 
tric Corliss  engine,  so  that  the  rocker  arms  and  wrist  plates  travel  equal 
distances  to  both  sides  of  their  central  positions. 

ADJUST  THE  STEAM  VALVE  RODS  so  that — when  the  steam  poppet  valve 
is  on  its  seat  and  the  steam  wrist  plate  is  in  its  extreme  position — there  is 
about  26  in.  clearance  at  the  latch  for  hooking  in. 

SET  THE  STEAM  ECCENTRIC  by  setting  the  engine  on  dead  center  and 
rotating  the  eccentric  on  the  shaft  in  the  direction  the  engine  is  to  run 
until  the  steam  valve  which  is  nearest  the  piston  has  ^2  in.  lead  or 
opening.  Then  tighten  the  eccentric,  to  the  shaft. 

ADJUST  THE  GOVERNOR  RODS,  with  the  governor  blocked  about  1  in. 
above  the  automatic  safety  stop  or  block  (Fig.  440),  so  that  cut-off  occurs 
in  equal  fractions  of  the  forward  and  return  strokes.  This  is  done  by 
adjusting  the  rods  connecting  the  knock-off  levers  of  the  head-end  steam 
valves  with  those  of  the  crank-end  steam  valves.  Then,  with  the 
governor  resting  on  the  safety  stop,  adjust  the  governor  rods  from  the 
governor  to  the  crank-end  valves  so  that  cut-off  takes  place  when  the 
steam  wrist  plate  has  nearly  reached  the  end  of  its  travel.  Cut-off  can  be 
observed  by  watching  for  the  spring-loaded  dash-pot  piston  to  drop  down. 

ADJUST  THE  EXHAUST  VALVE  RODS  so  that,  with  the  exhaust  wrist 
plate  in  its  central  position,  the  exhaust  cams  only  touch  the  steel  rollers 
on  the  exhaust-valve  stems.  The  cams  should  not,  in  this  position,  lift 
the  valves  from  their  seats. 

SET  THE  EXHAUST  ECCENTRIC  so  that  it  travels  about  60  deg.  behind 
the  crank.  In  order  to  increase  the  compression  and  provide  earlier 
release,  move  the  exhaust  eccentric  toward  the  crank  or  in  the  direction 
of  rotation.  Later  compression  and  release  are  provided  by  turning  the 


SEC.  210]  CORLISS  AND  POPPET  VALVES  191 

exhaust  eccentric  in  a  direction  the  reverse  of  that  in  which  the  engine 
runs. 

MAKE  FINAL  ADJUSTMENTS  FROM  INDICATOR  DIAGRAMS  as  with  all 
other  engines;  see  Sees.  112  and  175. 

QUESTIONS  ON  DIVISION  5 

1.  State  briefly  the  reasons  for  employing  Corliss  or  poppet  valves. 

2.  Under  what  conditions  might  it  not  be  advisable  to  use  an  engine  with  Corliss  or 
poppet  valves?     Why? 

3.  What  are  the  distinct  advantages  of  Corliss  valves? 

4.  What  features  distinguish  a  well-designed  Corliss  valve? 

5.  Explain  with  a  sketch  the  operating  mechanisms  used  with  positively-operated 
Corliss  valves.     What  variations  are  there? 

6.  State  the  advantages  and  disadvantages  of  positively-operated  Corliss  valves.     To 
what  kinds  of  engines  are  they  best  suited? 

7.  Illustrate  with  a  sketch  and  explain  the  operation  of  the  usual  detaching  Corliss- 
valve  releasing  mechanism. 

8.  Describe,  with  a  sketch,  the  entire  valve-operating  mechanism  of  a  detaching 
Corliss-valve  engine. 

9.  What  are  the  advantages  and  disadvantages  of  detaching  Corliss  valves? 

10.  Why  are  two  eccentrics  sometimes  employed  with  Corliss  valves?     Explain  fully 
the  limitations  of  using  only  one  eccentric. 

11.  What  is  the  cut-off  range  of  a  single-eccentric  Corliss  engine? 

12.  Into  what  three  classes  may  trip  gears  be  divided?     What  are  the  merits  of  each 
class? 

13.  What  is  the  principal  function  of  a  dash  pot  in  connection  with  a  trip  gear? 
What  secondary  function  has  the  dash  pot? 

14.  What  provision  should  be  made  in  the  valve  mechanism  to  prevent  inoperation 
of  the  engine  in  the  event  that  a  dash  pot  ceases  to  function? 

15.  What  are  the  principal  advantages  and  disadvantages  of  poppet  valves? 

16.  What  is  likely  to  cause  leaking  of  poppet  valves? 

17.  Explain,  with  slide  valve  analogies,  the  difference  between  single  and  double-beat 
poppet  valves. 

18.  Explain,  with  sketches,  the  operation  of  as  many  different  poppet-valve  operating 
mechanisms  as  you  can. 

19.  Take  the  sketch  made  in  answering  Question  8  and  explain  the  adjustment  of 
every  part  thereon  which  can  be  adjusted. 

20.  What  marks  are  necessary  in  setting  Corliss  valves?     Show  a  sketch.     If  these 
marks  did  not  appear  on  an  engine,  how  would  you  establish  them? 

21.  How  does  the  valve-setting  of  double-eccentric  Corliss  engines  differ  from  that  of 
single-eccentric  engines? 

22.  Is  it  advisable  to  try  to  lengthen  the  cut-off  of  a  Corliss  engine?     Why? 

23.  How  may  a  Corliss  engine  be  made  to  deliver  more  power? 

24.  Can  marks  be  used  to  advantage  in  setting  positively-operated  Corliss  valves? 

25.  In  the  absence  of  manufacturer's  instructions,  how  would  you  attempt  to  set  the 
valves  of  a  positively-operated  Corliss-valve  engine  which  has  a  shaft  governor,  has  its 
steam  valves  operated  from  a  gear  box  at  the  side  of  the  frame,  and  has  its  exhaust 
valves  driven  from  a  wrist  plate?     How  if  the  steam  valve  gearing  were  located  immedi- 
ately at  the  valve  bonnet? 

26.  How  would  you  set  the  admission  valves  of  a  uniflow  engine  which  are  operated 
by  overhead  reciprocating  cams  driven  by  a  shaft  governor? 

27.  How  would  you  set  poppet  exhaust  valves  which  are  operated  by  cams  which  are 
rotated  by  connectors  to  an  eccentric  on  the  main  shaft? 

28.  Describe  the  setting  of  poppet  valves  which  are  operated  from  a  lay  shaft. 

29.  Explain    the    construction    and    valve    setting    of    a    Corliss-gear    poppet-valve 
mechanism. 

30.  Explain  how  you  would  make  adjustments  to  correct  the  faults  which  are  revealed 
by  Figs.  102  and  103. 


DIVISION  6 

FLY-BALL  STEAM-ENGINE  GOVERNORS,  PRINCIPLES 
AND  ADJUSTMENT 

211.  A  Steam -Engine  Governor  (Fig.  247;  see  also  Sec. 
74  and  Fig.  52),  as  commonly  used  in  connection  with  a 
stationary  steam  engine,  is  a  device  for  keeping  the  speed  of 
the  engine  reasonably  constant.  A  properly  operating  gover- 


5 1 earn 

Hook- 

i Spring. 


Spindle  ,. 
Top- 


Governor 
Safety  - 
Sfop.p 
Governor  Dash- 


FIG.  247. — Governor  for  Corliss  engine.     (Harding  and  Willard,  MECHANICAL  EQUIP- 
MENT OF  BUILDINGS.) 

nor  "may  be  regarded  as  a  permanent  watchman,  overlooking 
the  'engine/  with  an  observant  eye.  If  more  power  is 
required,  it  (the  governor)  drops,  apparently  of  its  own  account 
and  lets  the  engine  take  more  steam ;  and,  as  the  load  decreases, 
it  rises  and  reduces  the  amount  of  steam  to  suit.  We  owe  this 

192 


SEC.  212J      FLY-BALL  STEAM-ENGINE  GOVERNORS 


193 


device  to  the  genius  of  James  Watt."  (From  IL  Hamkens, 
STEAM  ENGINE  TROUBLES.)  The  principle  of  Watt's  pendu- 
lum or  fly-ball  governor  is  still  widely  used  but  has  been  modi- 
fied to  meet  modern  conditions. 

NOTE. — A  GOVERNOR  Is  NOT  NECESSARY  UNDER  SOME  CONDITIONS 
(Graph  B,  Fig.  248),  such  as  in  marine  engine  service,  because  the  work 
done  by  such  an  engine  increases  rapidly  with  the  engine  speed.  There 


100 
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0       70    40    60    60    IOO  \7Q  I40  IfcO 
Load  In  Per  Cent  Of  Full  Load 

FIG.  248. — Graphs  showing  speed 
variation  with  load  of  governed  and 
ungoverned  engines. 


FIG.     249.  —  Simple     pendulum    or 
Governor. 


"Watt's" 


is  then  a  resultant  constant  speed  for  any  amount  of  steam  which  may 
be  admitted  to  the  engine.  But  in  most  stationary-engine  service 
(constant-speed  service)  the  load  may  vary  greatly  and  the  engine,  if 
not  governed  nor  regulated  by  hand,  would  slow  down,  whenever  the 
load  happened  to  increase;  or  "run  away"  whenever  the  loads  were 
diminished.  Hence,  for  such  service  a  governor  is  necessary. 

212.  The  Two  Principal  Kinds  Of  Steam-Engine  Governors 

(see  Sec.  74)  are:  (1)  Fly-ball  governors,  which  are  discussed  in 
this  division.  (2)  Shaft  governors,  which  are  discussed  in  Div. 
7.  A  fly-ball  governor  (Figs.  247,  249  and  250)'  is  one  which 
depends  for  its  action  (Fig.  252)  on  the  centrifugal  force 

13 


194     STE'AM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 


developed  in  two  or  more  weights  which  are  rotated  about  a 
(usually)  vertical  spindle  which  is  provided  for  the  purpose. 
Increased  rotational  speed. causes  the  weights  to  shift  radially 
from  the  spindle  axis  and  thereby  move  some  part  which  regu- 
lates the  amount  of  steam  admitted  to  the  engine  (Sec.  74). 

213.  Two  Forces  Are  Em- 
ployed By  Steam-Engine  Gov- 
ernors For  Detecting  Variations 
In  Engine  Speed  :  (1)  Centrifugal 
force.  (2)  Inertia  or  tangential 
inertia.  Centrifugal  force  is 
ordinarily  the  only  force  em- 
ployed in  fly-ball  governors  for 


fx£\ 

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L 

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Forces-, 

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n-  Side  View 


FIG.  250. — Governor  employing  hori- 
zontal tension  spring.  (Hamkens,  STEAM 
ENGINE  TROUBLES.) 


FIG.  251. — Showing  forces  developed  by 
a  revolving  governor  weight. 


detecting  speed  variations.  Inertia  is  employed,  as  will  be 
explained  in  Div.  7,  in  shaft  governors.  Note,  however,  that 
inertia  and  centrifugal  force  are  both  employed  in  such  gover- 
nors— never  inertia  alone.  Centrifugal  force  is  the  tendency 
of  a  rotating  body  to  move  away  from  its  axis  of  rotation.  In 
governor  design,  this  force  is  opposed  by  a  centripetal  force 


SEC.  214]      FLY-BALL  STEAM-ENGINE  GOVERNORS  195 

which  is  introduced  by  means  of  arms,  weights,  springs  or 
other  mechanism.  A  centripetal  force  is  one  which  opposes  a 
centrifugal  force ;  for  equilibrium  the  centripetal  force  must  be 
exactly  equal  and  opposite  to  the  centrifugal  force. 

EXPLANATION. — Consider  (Fig.  251)  a  ball,  B,  which  is  pivoted  at  M 
and  rotating  about  a  vertical  spindle,  S.  There  is  a  centrifugal  force,  C, 
tending  to  make  the  ball  move  out  radially  from  the  spindle,  S.  The 
ball  is  prevented  from  so  moving  by  a  spring,  N,  which  exerts  a  centri- 
petal force,  P,  just  equal  to  the  centrifugal  force.  If  the  ball  is  started 
suddenly,  it  tends  to  "hang  back"  and  exerts  a  force,  /,  due  to  its  inertia. 
If  the  ball  is  stopped  suddenly,  it  tends  to  continue  moving  and  exerts 
a  force,  /',  also  due  to  inertia. 

214.  All   Fly-Ball   Governors   Permit   Some   Variation  In 
Engine  Speed. — It  has  been  found  impractical  to  endeavor  to 
maintain  the  speed  of  an  engine  exactly  constant.     It  will  be 
noted  from  subsequent  descriptions  of  governor  operation  that 
the  governor  does  not  change  its  position  until  a  change  in 
speed  occurs;  hence,  it  is  evident  that  a  speed  change  is  neces- 
sary to  cause  a  governor  to  operate.     There  is,  moreover, 
when  an  engine  is  properly  governed,  a  definite  speed  corre- 
sponding to  each  load,  that  is,  the  speed  varies  with  the  load. 
The  graph  A  (Fig.  248)  is  characteristic  of  this  sort  of  per- 
formance.    The  speed  variation  from  no  load  to  overloads  may 
be  made  very  small  if  so  desired.     Variation  in  speed  of  5  per 
cent,  over  the  working  range  of  the  engine  is  often  permissible. 
Variations  as  low  as  1  per  cent,  of  the  mean  engine  speed  may 
be  obtained  under  favorable  conditions. 

215.  There  Are  Two  Principal  Methods  Used  With  Fly- 
Ball  Governors  For  Controlling  The  Steam  Admitted  To  An 
Engine :  (1)  By  throttling  (Figs.  252  and  253)  or  reducing  the 
pressure  in  the  steam  chest  of  the  engine  by  partly  closing  a 
valve  in  the  live-steam  line.     With  this  method,  the  governor 
(Fig.   254)   is  not  part  of  the  valve-operating  mechanism. 
This  method  of  governing  is  used  chiefly  with  simple  slide- 
valve  engines.     (2)  By  varying  the  cut-off.     Under  this  condi- 
tion, the  governor  (Figs.  247,  255,  and  256)  is  part  of  the  valve 
gear.     This  method  of  governing  is  employed  chiefly  with 
Corliss  and  poppet-valve  engines. 


196     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE      [Div.  6 

EXPLANATION. — Fig.  253  shows  the  effect  on  the  indicator  diagram  of  a 
slide-valve  engine  of  a  throttling  governor  such  as  that  of  Fig.  254. 
The  line,  A ,  represents  the  admission  and  expansion  with  a  large  governor- 
valve  opening.  B  and  C  correspond  to  smaller  governor-valve  openings 
at  lighter  loads.  It  will  be  noted  from  the  way  in  which  the  admission 


Governor  /n  No~ 
Load  Posit  ion 


I-Full-Load,  Governor 
Valve  Open 


///////////////////////// 
-No-Load,  Governor  Valve 
Nearly  Closed 


Fia.  252. — Diagram  illustrating  method  of  governing  by  throttling, 
matic  construction  shown  above  is  never  used.) 


(The  diagram- 


lines  slope  from  points  R,  S  and  T,  that  there  is  considerable  throttling 
(wire  drawing  or  pressure  drop  due  to  friction)  of  the  steam  in  the  governor 
valve.  This  throttling  results  in  loss  in  effective  steam  pressure  (Sec.  14) 
and  consequent  poor  economy  especially  at  light  loads.  Fig.  256  shows 
the  effect  of  a  cut-off  governor  such  as  that  shown  in  Fig.  247,  on  the 


•Atmospheric  Pressure 


FIG.  253. — Indicator  diagrams  at  various  loads  taken  from  an  engine  governed  by 

throttling. 

indicator  diagrams  of  a  Corliss  engine.  The  cut-off  occurs  at  A,  Bt  C 
and  D  (Fig.  256)  at  various  loads.  The  engine  performance  here  shown 
is  much  superior  to  that  in  Fig.  253.  The  admission  lines  are  nearly 
horizontal  indicating  that  there  is,  at  all  loads,  but  little  steam  friction 
in  the  valves. 


SEC.  215]      FLY-BALL  STEAM-ENGINE  GOVERNORS 


197 


'Oil  Governor 
Here 


Hemispherical 
Weigtrfs- 


Weight- 
Carrying 
Spindle-. „ 

Spring  Adjust  men  t 
For  D/fferenf 
Speeds 


Spring  For 
Closing  Thrott 
WhenSafefy 
Lever  /s 
Dropped 


FIG.  254. — Erie  pump  governor.  (This  governor  is  used  on  pumping  engines  where, 
besides  limiting  the  maximum  engine  speed,  it  must  control  the  engine  speed  to  meet  the 
demands  of  the  pump.  That  is,  if  less  pumping  is  required,  the  governor  diminishes  the 
engine  speed.  Thus,  it  will  control  the  engine  at  speeds  of  80  to  320  r.p.m.,  depending 
upon  the  demand.  If  the  belt  breaks,  the  idler,  7,  drops  allowing  the  valve  to  be  closed 
by  the  spring,  S,  through  the  safety  latch,  M,  and  lever,  L.) 


198    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 

216.  A  Steam -Engine  Governor  Should  Be  Designed  And 
Maintained  For  The  Greatest  Possible  Safety  And  Reliability. 
A  "safety  stop"  should  be  provided  in  every  case.  Belt- 


G  over  nor  In 
Full-Load  Position. 


Knock-Off  Block 
Js  Con1rv/ fed  By 
Governor 
,'    Governor- 
Sleeve 
Controls 
Lever 


Supply 


I-Full-Lodd  Position;  Cut-Off 
Has  Not  Occured  At  One- 
Fourth  Stroke 


Steam 
Supply 
Crank  Operates  Va/ve 

Through  Linkage 
E- No-Load  Position;  Cut-Off 
Occurs  Before  One-Fourth 
Stroke 


FIG.  255. — Diagram  illustrating  method  of  governing  by  varying  the  cut-off.  (The 
"knock-off"  principle  illustrated  above  is  employed  extensively  in  the  Corliss  governing 
mechanism;  but  the  diagrammatic  simplified  construction  shown  above  is  never  used.) 

driven  governors  are  commonly  provided  with  safety  idlers 
(7,  Figs.  254  and  257)  so  that,  if  the  belt  breaks,  the  idler  will 
drop  and  shut  the  governor  valve.  Corliss  governors  (Fig.  247) 


A     B 


Atmospheric  Pressure?* 
_  k"Zero  Pressure 


FIG.  256. — Indicator  diagrams  taken  at  various  loads  from  engine  governed  by  changing 

cut-off. 


are  provided  with  safety  knock-off  cams,  C,  so  that,  in  case 
the  governor  drive  fails  and  the  balls  drop,  the  intake  valves 
will  admit  no  steam  to  the  engine.  Various  arrangements 


SEC.  216]      FLY-BALL  STEAM-ENGINE  GOVERNORS 


199 


(Fig.  258)  are  provided  for  holding  the  governor  out  of  the 
safety  position  while  starting  the  engine.  Whatever  arrange- 
ment is  used,  it  must  be  so  designed  that  it  will  fall  out  of  the 
way  automatically  as  soon  as  the  governor  lifts  (Fig.  258). 
The  engineer's  memory  should  not  be  trusted  to  remove  the 
starting  cam  or  lever.  Pins  (P,  Fig.  259),  which  must  be 
removed  by  hand  after  starting,  should  not  be  tolerated. 


FIG.  257. — Elevation  of  Pickering  governor  showing  safety  idler  feature. 

NOTE. — MANY  ENGINES  AND  POWER  PLANTS  HAVE  BEEN  WRECKED 
DUE  To  GOVERNOR  FAILURES.  If  the  governor  does  not  shut  off  nearly 
all  the  steam  when  the  load  is  taken  off  the  engine,  the  engine  speed  may 
become  great  enough  to  burst  the  flywheel  by  centrifugal  force.  Some- 
times a  "secondary  safety  stop"  (Fig.  260)  is  installed  in  addition  to  the 
one  with  which  the  governor  is  regularly  equipped. 


200    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 


NOTE. — AN  ENGINE,  WHICH  lp  EQUIPPED  WITH  A  SAFETY  DEVICE, 
MAY  STOP  WHEN  AN  EXCESSIVELY  HEAVY  LOAD  Is  THROWN  ON  IT 
(W.  H.  Wakeman  in  Power}.  In  almost  all  makes  of  Corliss  engine 


-Load  Or 
Counterpoise 


Weight 
(Starting  Lever  ) 


•Position  When 
Starting 

•Position  When 
Running 


FIG.  258.  —  Showing  starting 
lever,  L,  which  falls  out  of  position 
when  the  governor  lifts. 


.-Drop  Rod 
From  Governor 


Governor 
'o/umn 


Pin-' 


Governor  CoJumn'' 

FIG.  259.  —  Showing  unsatisfactory  pin 
arrangement  for  holding  Corliss  governor  in 
starting  position.  This  arrangement  is  unsafe. 


governors  there  is  the  "safety  pin"  on  which  the  weights  are  brought  to 
rest  when  the  mechanism  is  not  in  action.  Or  instead  a  "safety  collar" 
may  be  used.  Both  of  these  devices  prevent  the  mechanism  from  falling 


Primary  (Throttling) 
Governor*-*^ 


,Steam  Line 
fo  Engine 


.-Belt-  Wheef 
Rim 

Governor 
Belt 
Pulley-- 


Trip 
Rod 


'  Throttle 
Valve 


"  ~70  Engine 


'^Centrifugal 
Tripping  Device 

FIG.  260. — Detail  of  the  design  of  trigger  device  for  secondary  speed  control  on 
Chandler  &  Taylor  variable-speed  engines.  (If  speed  becomes  excessive,  T  is  thrown 
outward  by  centrifugal  force,  compressing  S.  Thereby  C  is  tripped  which  releases  R. 
Then  W  falls  down  and  closes  V  which  shuts  off  steam  to  the  engine.) 


so  low  that  no  steam  will  be  admitted.  These  pins,  or  collars,  are  so 
placed  that,  when  it  is  at  rest,  the  engine  will  get  steam.  When  the 
engine  is  in  full  operation,  the  pin  is  removed  or  the  collar  so  turned  that, 


SEC.  217]      FLY-BALL  STEAM-ENGINE  GOVERNORS 


201 


should  the  belt  or  gear  break,  the  governor  mechanism  will  drop  so  low  as 
to  cut  off  all  steam  and  a  shut-down  results.  In  plants  where  heavy  and 
changing  loads  are  handled,  it  is  not  uncommon  for  a  sudden  load  to  be 
imposed  on  the  engine,  which  is  so  great  as  to  make  the  mechanism  drop 
low  enough  to  shut  off  steam,  if  the  operator  has  attended  to  his  duty  of 
removing  the  pin  or  setting  the  safety  collar  after  starting  up.  The  result 
is  a  shut-down.  This  may  confuse  the  inexperienced  operator  until  he 
knows  the  cause.  Always  look  at  the  "safety"  when  an  unusual  shut- 
down occurs. 

NOTE. — SOME  GOVERNOR  PULLEYS  ARE  SECURED  To  THE  SHAFT  WITH 
A  SET-SCREW  WHICH  MAY  COME  LOOSE,  or  a  key  may  work  loose.  The 
pulley  may  hold  just  enough  to  slowly  rotate  the  governor  but  not  suffi- 
ciently to  bring  it  up  to  speed.  The  result  will  be  a  runaway  engine. 
An  oily  or  slack  governor  belt  may  also  cause  this. 

217.  Only  The  Best  And  Safest  Materials  And  Methods 
Should  Be  Used  In  The  Construction  Of  Governor  Mechanisms. 


5houfcferect 


I-Straight 
Key 


- Taper   Key 


FIG.  261. — Showing  methods  of  securing 
governor  pulleys. 


FIG.  262. — Showing  a  method  of 
curing  a  governor  lever. 


The  cost  of  these  materials  and  methods  is  comparatively 
small,  whereas  the  damage  done,  if  the  governor  fails,  may  be 
very  large.  Governor  belts  should  be  of  the  best  grade  and  be  so 
sewed  and  cemented  as  to  be  practically  endless.  They 
should  be  of  even  weight  and  not  wide  enough  to  rub  on  the 
flanges  of  the  governor  pulleys.  Governor  pulleys  should 
preferably  be  of  metal  and  secured  with  more  than  a  single 
set-screw.  Pulley  faces  and  belts  should  be  kept  free  of  oil 
which  might  cause  slipping.  Recommended  fastenings  for 
governor  pulleys  and  levers  are  shown  in  Figs.  261  and  262. 
218.  Dangers  Due  To  The  Binding  Of  A  Governor  Mechan- 
ism Should  Be  Carefully  Avoided. — The  pivots  of  governor 


202    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 


rods  should  have  sufficient  end  play  (E,  Fig.  263)  to  prevent 
binding  caused  by  slight  frame  movements  or  by  grit  getting 
between  the  end  faces.  The  governor,  if  new  or  if  it  has  been 


Spindle 


'Collar 


Pivot  Pin 


'Counterpoise 
-Yoke 


FIG.    263. — Showing    proper    end-play    for         FIG.  264. — A  collar  which  limits  the  lift 
governor-rod  pivots.  of   a   fly-ball   governor   should  never  be 

allowed  to  get  too  low. 

out  of  use  for  some  time,  should  be  moved  by  hand  before 
starting  to  insure  that  it  does  not  bind.  Collars  (C,  Fig.  264) 
must  not  limit  the  movement  of  the  governor  so  as  to  prevent 


•Casing 


JL;  -Spindle 
FIG.  265. — Enclosed-spring  governor.     (From  Hamkens,  STEAM  ENGINE  TROUBLES.) 

its  completely  shutting  off  the  steam  supply.  Enclosed 
parts  (such  as  dash-pots,  Sec.  230,  and  enclosed  springs, 
Fig.  265)  should  be  inspected  regularly.  Oil  should  occasion- 
ally be  drained  from  dash-pots  and  the  pots  refilled  with  clean 


SEC.  219]      FLY-BALL  STEAM-ENGINE  GOVERNORS  203 

oil.  The  pots  should  be  kept  well  filled  with  oil  as  pocketed 
air  is  likely  to  cause  dangerous  racing. 

219.  Various  Terms  Used  To  Describe  The  Performance 
Of  A  Governor  may  be  defined  as  follows :  (1)  By  sensitiveness 
is  meant  the  ability  of  a  governor  to  substantially  vary  the 
amount  of  steam  admitted  to  the  engine  in  response  to  slight 
changes  in  engine  speed.  Sensitiveness  is  not  an  exact  term 
(see  below).  (2)  By  powerfulness  of  a  governor  is  meant 
the  force  which  the  rotating  parts  of  the  governor  are  capable 
of  exerting  on  the  governor  rods  or  other  steam-controlling 
mechanism  when  a  variation  in  speed  occurs.  If  a  governor 
is  to  be  very  sensitive,  and  very  powerful,  it  must  be  very 
large  or  run  at  a  high  speed.  (3)  Promptness  is  the  ability 
of  the  governor  to  respond  quickly  to  load  changes.  A  very 
prompt  governor  is  one  which  requires  only  a  fraction  of  a 
second  to  adjust  itself  to  a  considerable  change  in  load. 
(4)  Sluggishness  is  the  opposite  of  promptness.  A  governor 
which  requires  a  half  minute  or  more  to  adjust  itself  to  a 
new  load  is  relatively  ''sluggish.''  To  be  very  prompt,  a 
fly-ball  governor  must  not  be  heavy.  (5)  Coefficient  of 
regulation,  also  called  regulation,  coefficient  of  speed  regulation, 
speed  variation  or  fluctuation,  is  the  variation  in  speed  which 
the  governor  permits  from  no  load  to  full  load  expressed  as  a 
percentage  of  the  full-load  speed.  The  coefficient  of  regula- 
tion is  an  exact  mathematical  measure  of  sensitiveness. 
Expressing  this  relation  by  a  formula: 

(25)  Mr  =  ^P^'  (decimal) 

Wherein:  Mr  =  the  regulation  coefficient,  expressed  deci- 
mally. Nn  =  speed  of  the  engine  at  no  load,  in  revolutions 
per  minute.  N/  =  speed  of  the  engine  at  full  load,  in  revolu- 
tions per  minute. 

EXAMPLE. — An  engine  manufacturer  guarantees  a  regulation  coefficient 
of  1.5  per  cent,  for  his  engine  equipped  with  a  certain  governor.  The 
engine  makes  178  r.p.m.  at  no  load  and  175.7  r.p.m.  at  full  load.  Is  it 
within  the  guarantee?  SOLUTION. — By  For.  (1)  the  coefficient  of  regula- 
tion, Mr  =  (Nn  -  Nf}/Nf  =  (178  -  175.7)  -r-  175.7  =  0.0141  =  1.41  per 
cent.  The  engine  is  within  the  guarantee. 


204     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 

NOTE. — IN  CONDUCTING  REGULATION  GUARANTEE  TESTS,  it  is  usually 
understood  that  the  change  from  no  load  to  full  load  is  to  be  made 
gradually.  But  "specifications  should  clearly  state  the  method  to  be 
employed  in  determining  the  speed  variation  and  basis  upon  which  the 
calculations  are  to  be  made.  This  is  particularly  important  when  the 
unit  is  supplying  both  a  lighting  and  rapidly  fluctuating  motor  load,  as 
in  this  case  the  instantaneous  variation  of  speed  must  be  limited  to  a  small 
margin  to  prevent  'blinking'  of  the  lights.  For  high-speed  direct- 
connected  units  the  U.  S.  Treasury  Department  specifies  that  the  maxi- 
mum variation  in  speed  for  a  slow  change  in  load  from  no  load  to  full  load 
or  vice  versa  shall  not  exceed  1^  per  cent,  of  the  speed  at  full  or  normal 
load,  and  that  for  sudden  change  in  load  the  maximum  variation  shall 
not  exceed  2  per  cent."  (From  Harding  and  Willard,  MECHANICAL 
EQUIPMENT  OF  BUILDINGS.) 

220.  Some  Descriptive  Terms  Applied  To  Fly-Ball  Gover- 
nors which  should  be  understood  are:  (1)  A  stable  or  static 
governor  is  one  which  occupies  a  definite  position  at  a  definite 
speed.     A  governor  is  stable  when  the  resistance  to  motion 
(centripetal  force)  changes  faster,  as  the  balls  assume  different 
positions,   than  does  the  centrifugal  force  which  the  balls 
develop.     (2)  An  unstable  or  astatic  governor  is  one  in  which  a 
slight  increase  or  decrease  in  speed  will  cause  it  to  move  to  one 
or  the  other  extreme  position.     If  the  restraining  (or  centri- 
petal) force  changes  more  slowly  than  the  centrifugal  force, 
a  governor  is  unstable.     (3)  A  neutral  or  isochronous  governor 
is  one  which,  at  a  certain  speed,  assumes,  indifferently,  any 
position  throughout  its  range.     If  the  centrifugal  force  and  the 
centripetal  force  change  at  the  same  rate,  the  governor  is 
neutral  or  isochronous. 

NOTE. — AN  UNSTABLE  GOVERNOR  Is  QUITE  USELESS  FOR  ENGINEER- 
ING PURPOSES.  Such  a  governor  would  always  be  either  in  full-load 
position  or  shut  off  entirely.  Governors  are  frequently  called  "isochron- 
ous" (which  means  equal  speed)  when  they  are  not  truly  so.  A  truly 
isochronous  governor  would  also  be  useless  for  engineering  because  it 
would  change  in  position  as  much  for  a  slight  change  in  load  as  it 
would  for  a  large  one.  The  aim  in  governor  design  should  be  to  make  the 
governor  stable  but  very  nearly  neutral,  that  is,  to  make  it  as  nearly 
isochronous  as  is  feasible.  Such  a  governor  gives  smaller  speed  variation 
than  does  a  very  stable  governor. 

221.  The   Action    Of   Centrifugal   Force   In   Actuating   A 
Governor  is  considered  in  Sees.  222  and  224.     While  a  knowl- 


SEC.  222]      FLY-BALL  STEAM-ENGINE  GOVERNORS 


205 


edge  of  these  principles  is  of  interest  to  the  practical  man,  it  is 
not  probable  that  he  will  ever  have  to  apply  them  in  adjusting 
or  maintaining  an  engine  governor.  However,  a  knowledge  of 
these  principles  and  their  application  is  essential  to  the 
governor  designer. 

222.  To  Compute  The  Centrifugal  Force  Developed  In  A 
Revolving  Governor  Weight,  use  the  following  formula: 
(26)  Fc  =  0.000,028,5Wr;]V2  (pounds) 

Wherein:  Fc  —  the  centrifugal  force,  in  pounds,  developed  by 
the  weight.  W  =  the  weight  of  the  governor  ball,  in  pounds. 


2Lb. 


Arms  Of 
Different  Lengths 


--T*  -Pivot 


Yoke. 

Spindle-. . 


inks 
-Sleeve 


Neglect  The  Weight 
Of  The  Levers,  Links, 
And  Sleeve 

FIG.  266. — How  much  tension 
is  there  in  the  spring? 


Different  Weights 


FIG.  267. — Showing  constant  height  to  which 
governor  balls  will  rise  at  a  certain  speed. 


N  =  the  speed  of  the  governor,  in  revolutions  per  minute. 
Ti  =  the  radius  from  the  center  of  gravity  of  the  weight  to  the 
axis  of  rotation  (center  of  the  spindle),  in  inches. 

EXAMPLE. — Assume  that  the  balls  of  the  governor  (Fig.  266)  weigh 
2  Ib.  each  and  are  10  in.  from  the  center  of  the  spindle  when  they  are 
revolving  at  250  r.p.m.  What  centrifugal  force  will  they  exert  on 
the  spring  under  these  conditions?  SOLUTION. — By  For.  (26),  the 
centrifugal  force  in  each  ball  equals  the  tension  on  the  spring,  or:  Fc  = 
0.000,028,5Wr,-#2  =  0.000,028,5  X  2  X  10  X  (250)2  =  35.6  Ib. 

223.  The  Theoretical  Vertical  Distance  Between  The  Center 
Of  The  Balls  And  The  Pivot  Of  The  Arms  In  A  Simple  Pendu- 
lum Governor  Depends  On  The  Angular  Speed  And  Is  Inde- 
pendent Of  All  Other  Factors. — Assume  that  three  balls, 
BI,  B2  and  £3  (Fig.  267),  of  different  weights  are  suspended  by 
arms  of  different  lengths  and  caused  to  make  the  same  number 
of  revolutions  per  minute  about  a  common  spindle,  S.  The 
vertical  height,  H,  will  be  the  same  for  all  three  regardless  of  the 


206     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 


weights  of  the  balls  and  lengths  of  the  arms.  The  statements 
of  this  section  are  true  only  for  an  ideal  governor  mechanism 
which  has  weightless  arms  and  which  has  nothing  to  lift  when 
it  operates.  If  the  governor  balls  must,  when  they  rise,  lift 
a  weight  other  than  their  own  then  they  will  not  rise  as  far  as 
they  would  rise  if  unweighted.  See  Sec.  225  for  effects  of 
weighting. 

224.  To  Compute  The  Theoretical  Height  To  Which  The 
Balls  Of  An  Ideal  Simple  Pendulum  Governor  Will  Rise  At  A 
Given  Speed,  use  the  following  formula: 


(27) 


Lt,  = 


(inches) 


Simple  Pendulum  Governor 


Loaded 
Governor — /^ 
Positions 
The  Load  Weighs 
Times  As  Much 
As  One  Ball ) 


;'60r.p.m.  "I?   120r.p.m. 

'Weight  of  Arms  and 
Sleeve   May  be 
Neglected 

FIG.    268. — How    high  FIG.  269. — Showing    theoretical   positions  of   balls  of 

will  the  balls  rise?  simple    and    of    loaded  governors    at    different    speeds. 

(Arms   are    assumed   to   be    weightless.     The  bails   lift 

nothing    but    themselves   and,    if    specified,   a  centrally 

attached  load.) 

Wherein:  Lhi  =  the  height,  in  inches,  from  the  center  of 
gravity  of  the  balls  to  the  pivot  of  a  simple  pendulum  governor. 
N  =  the  speed  of  the  governor,  in  revolutions  per  minute. 

EXAMPLE. — Compute  the  height  from  the  center  of  gravity  of  the  balls 
to  the  pivot  of  the  governor  balls  shown  in  Fig.  268  when  it  is  revolving 
at  60  r.p.m.;  at  120  r.p.m.  SOLUTION. — By  For.  (27),  the  height, 
Lhi  =  35,200/N2  =  35,200  ^-  3,600  =  9.8  in.  at  60  r.p.m.  Lhi  =  35,200  H- 
14,400  =  2.44  in.  at  120  r.p.m. 

NOTE. — THE  SIMPLE  PENDULUM  GOVERNOR  MUST  RUN  AT  Low  SPEEDS 
since  the  balls  would  fly  out  to  a  nearly  horizontal  position  at  high  speeds 


SEC.  225]      FLY-BALL  STEAM-ENGINE  GOVERNORS 


207 


I -Loaded  Watt         H- Porter 
.-•Spm 


and  would  then  change  very  little  in  position  while  the  speed  varied  greatly  ; 
that  this  is  true  is  evident  from  the  preceding  example.  Fig.  269  shows 
the  theoretical  angular  positions  of  a  simple-pendulum-governor  arm 
at  different  speeds.  The  practical  speed  limit  for  simple-pendulum 
governors  is  about  125  r.p.m.  while  speeds  of  600  r.p.m.  and  over  are  used 
in  spring-loaded  fly-ball  steam  engine  governors.  Actual  governor  balls 
do  not  ordinarily  rise  as  high  as  indicated  by  Fig.  269  because  of  the 
restraining  gravitational  forces  of  the  mechanisms  or  weights  which 
must  be  lifted  by  the  balls. 

225.  Nearly  All  Modern  Fly-Ball  Governors  Are  Weight-  Or 
Spring-Loaded. — Hence  they  will  not  rise  to  the  theoretical 
heights  given  by  For.  (27.)     Watt's  unloaded  governor  (Fig. 
249)  was  satisfactory  for  slow-speed 

engines  which  did  not  require  close 
speed  regulation,  but  for  most  mod- 
ern requirements,  it  is  unsatisfac- 
tory. Fig.  270  shows  various 
methods  of  applying  a  weight  load, 
W,  or  counterpoise  to  a  fly-ball 
governor.  In  all  of  these  methods 
the  weight  is  so  arranged  that  it 
will  slide  on  the  spindle  and  revolve 
with  the  spindle  and  balls.  The 

Weight,  in  all  Cases,  Opposes  the  FIG.  270.— Various  arrange- 
,  ,  ,.  , ,  ,  „  n  ments  used  in  applying  a  weight 

tendency  of  the  balls  to  fly  apart.  ]oad  or  counterpoise  to  a  gover- 
These  arrangements  give  more  accu-  nor^  ™  =  weight  or  counterpoise, 
rate  regulation  than  can  be  obtained 

with  an  unloaded  governor  because,  with  them,  a  small  change 
in  engine  speed  can  be  made  to  cause  a  large  change  in  gov- 
ernor position  (Fig.  269). 

226.  The  Advantages  Of  The  Spring-  Or  Weight-Loaded 
Governor    Over    The  Simple  Pendulum  Governor  may  be 
enumerated  as  follows:     (1)  It  increases  the  range  of  speed 
between  maximum   and   minimum  governor  positions      (2) 
It  affords  closer  regulation  by  increasing  the  vertical  move- 
ment (Fig.  269)  for  a  given  change  in  speed.     (3)  It  decreases 
the  sluggishness  of  the  governor  by  making  it  possible  to  employ 
light-weight  balls.     (4)   It  increases  the  sensitiveness  of  the 
governor    by   furnishing   an   effective    means    of    offsetting 
frictional  resistances.     The  governor  is  made  more  powerful 


208     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 

and,  thus,  more  easily  overcomes  frictional  resistances  in  its 
own  mechanism. 

227.  The  Following  Formula  Expresses  The  Relation, 
For  A  Porter  Governor,  Between  Speed,  Height,  And  Weights 
Of  Balls  And  Counterpoise. — This  formula  assumes  that  the 
four  arms  of  the  governor  are  of  equal  length. 

w  +  Wi  w  35,200 
(28)  Lhi  = ^—     X  ~~-  (inches) 

Wherein:  Lhi  =  the  height  (Lhi,  Fig.  271)  from  the  center  of, 
the  balls  to  the  intersection  of  the  arm  and  spindle  axes,  in 
inches.  W  =  the  weight  of  one  of  the  two  balls,  in  pounds. 
Wi  =  the  weight  of  the  central  load  or  counterpoise,  in 
pounds.  N  =  the  speed  of  the  governor,  in  revolutions  per 
minute. 

EXAMPLE. — What  does  the  counterpoise  of  a  Porter  governor  (Fig.  271) 
weigh  if  the  balls  weigh  8.3  Ib.  each  and  the  height  is  13  in.  at  325  r.p.m.  ? 
SOLUTION. — Substituting  in  For.  (28),  there  results:  13  =  [(8.3  + 
Wi)  •*-  8.3]  X  35,200  -*•  (325) 2,  from  which  Wi  + 
8.3  =  323.7  or  Wl  =  315  Ib. 

NOTE. — THE  RELATIONS  OF  FORCES,  WEIGHTS 
AND  SPEEDS  IN  FLY-BALL  GOVERNORS  are  indi- 
cated in  the  following  items.  The  matters  of 
rates  of  increase  and  decrease  of  centrifugal  and 
centripetal  forces  in  governors  of  various  types 
in  various  positions  will  not  be  discussed  in  detail 
Porter  ^J  in  this  book  since  they  involve  higher  mathe- 

Governor  TT  .       .       ,, 

matics  and  are  of  interest  principally  to  governor 
325 a  r.p.m.  designers.     Also    the  methods   of   analyzing   the 

FIG.  271.— How  much   forces   in   a   governor  (as  used  in  the  above  ex- 
does  the  central  load  or    ample)  will  not   be  explained  for  somewhat  the 

counterpoise  weigh/ 

same  reason. 

(1)  The  lifting  forces  exerted  by  governor  balls  in  a  loaded  governor  are 
usually  many  times  greater  than  the  weights  of  the  balls. 

(2)  The  centrifugal  force  of  the  balls  is  proportional  to  the  weight  of 
the  balls,  to  the  distance  of  the  balls  from  the  spindle  and  to  the  square 
of  the  speed;  see  For.  (26). 

(3)  The  faster  a  given  set  of  governor  balls  revolves,  the  greater  must 
be  the  load  applied  to  balance  them. 

(4)  The  greater  the  load  for  a  given  set  of  balls,  the  more  powerful 
(Sec.  219)  the  governor,  provided  it  goes  fast  enough  to  lift  the  load. 

(5)  Other  things  being  equal,  a  high-speed  heavily-loaded  governor 
is  more  prompt  and  more  sensitive  than  a  low-speed  one. 


SEC.  228]      FLY-BALL  STEAM  ENGINE  GOVERNORS 


209 


(6)  All    weight-loaded    gover- 
nors of  the  types  shown  in  Fig. 
270  are  stable  except  the  cross- 
arm   type  which  may  be  so  de- 
signed    as     to    be   unstable  or 
astatic.     Extra  attachments 
may    be    added     to    any   gov- 
ernor so  as  to  lessen  or  increase 
its  stability. 

(7)  Governors    of    the    types 
shown  in  Fig.  270  become  less 
powerful  and  sensitive  as  their 
arms  approach  nearly-horizontal 
positions. 

(8)  The  smaller  the  speed  regu- 
lation, the  less  powerful  will  be  a 
given  set  of  governor  weights  or 
balls  revolving  at  a  given  speed. 

228.  Spring-Loaded  Gov- 
ernors May  Secure  Close 
Regulation  And  Are,  In 
General,  More  Prompt 
Than  Weight-Loaded  Gov- 
ernors.— The  inertia  of  a 
spring  is  negligible  and  so 
only  the  inertia  of  the 
weights  and  arms  need  be 


Main 
Compression 

Spring 


Knife 
'Edge 


Driving 
Gear 

Bearing 


Spindle- 


FIG.  272. — Spring   arrangement  used 
in  the  Gardner  throttling  governor. 


14 


FIG.  273. — General  arrangement  of  No.  7 
open  Tolle  governor.  (Vilter  Mfg.  Co., 
Milwaukee,  Wis.) 


210     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE      [Div.  6 

overcome  when  a  spring-loaded  governor  changes  position. 
With  a  given  governor  design,  a  stiffcr  spring  slightly  com- 
pressed gives  a  more  stable  and  prompt  (but  less  sensitive) 
governor  than  does  a  weaker  (more  flexible)  spring  more 
heavily  compressed.  A  spring-loaded  governor  is  usually 
stable  because  the  resistance  of  a  spring  rapidly  increases  as 
the  force  on  it  is  increased.  Figs.  257,  265,  272,  and  273  show 
various  arrangements  by  which  spring  loads  may  be  applied 
to  fly-ball  governors. 

229.  A    Governor   Which   Has    Small    Speed    Regulation 
Must  Be  Provided  With  Some  Means  Of  Preventing  "Hunt- 


c 

,  —f 

•'- 

^  — 

—  h^ 

\ 

—  J 

* 

^  — 

:.:' 

D 



y 

-Li 

'//* 

/r 

C//C 

n 

II 

^ 

\ 

1     O 

i 

— 

—  D 

A 

TT 

Much  Mechanical  Friction~ 

TTT 

-><• 

—  B  — 

3 

i 

2 

/ 

A 

—t£— 

111  •  Proper  Fluid  //"/c  tion 

FIG. 


05      10     15    20    25    30    35    40  45 
Time     In    Seconds 

274. — Showing  characteristic  "Hunting" 
graphs  of  governors. 


'P/vof 
Support 


FIG.  275. — Non-adjustable  governor 
dash-pot  filled  with  oil. 


ing." — A  governor  hunts  when,  in  changing  from  one  load 
to  another,  it  has  a  tendency  to  go  too  far  due  to  the  momen- 
tum of  its  parts. 

EXPLANATION. — Fig.  274-7  shows  the  "hunting"  of  a  very  free-moving 
governor  when  the  load  changes  suddenly.  Assume  that  the  governor 
was  steady  in  position  A  A'  for  a  certain  load  and  that  the  load  changes 
so  that  the  governor  should,  for  equilibrium,  assume  some  new  position 
B'B.  The  governor  responds  but  the  momentum  of  its  parts  carries 
it  past  the  proper  position  to  C  and  then  back  to  D.  This  action  may 


SEC.  230]      FLY-BALL  STEAM-ENGINE  GOVERNORS 


211 


•Piston 


cause  the  engine  to  pull  unevenly  and  the  "hunting"  may  then  be  further 
increased.  Graph  //  shows  the  effect  of  much  mechanical  friction  on  the 
governor  action.  The  governor  then  hunts  very  violently  and  in  "jerks  " 
but  the  action  may  be  very  uncertain  and  cause  much  variation  in  engine 
speed.  Graph  III  shows  the  effect  of  fluid  friction  introduced  by  means 
of  a  properly  adjusted  dash-pot  (Figs.  275  and  276).  The  governor  tends 
to  follow  graph  /  (Fig.  274)  but  the  fluid  friction  in  the  dash-pot  prevents 
its  so  doing.  The  governor  soon  comes  to  rest  at  E.  Fluid  friction 
prevents  rapid  movement  but  offers  practically  no  resistance  to  very  slow 
motion.  This  friction  therefore  prevents  "hunting"  and  sudden  move- 
ments but  does  not  materially  decrease  the  accuracy  of  the  the  governor. 

230.  A  Dash-Pot  Or  Gagpot  (Figs.  275  and  276)  is  usually 
used  to  limit  the  rate  at  which  a  cut-off  governor  may  move. 
The  valve  of  a  throttling  governor  has  a  stabilizing  (or  damp- 
ing) effect  so  that  a  dash-pot  is  not  ordinarily  necessary  with 
governors  of  the  throttling  type.  The 
dash-pot  consists  (Fig.  276)  of  a  cylinder 
C  filled  with  oil;  a  piston  P,  and  rod  R 
and  means  such  as  pipe  B  for  allowing 
oil  to  flow  around  the  piston  at  the 
proper  rate.  Simple  non-adjustable 
dash-pots  (Fig.  275)  have  holes  for 
allowing  oil  to  pass  through  the  piston. 
Movable  plates  are  sometimes  placed 
over  these  holes  and  controlled  by  a 
nut  on  the  piston  rod.  A  pet-cock  is 
usually  provided  for  draining  and  a  hole 
for  filling.  If  the  dash-pot  piston  rod 
is  directly  connected  to  a  lever,  as  in 
Fig.  250,  the  dash-pot  cylinder  should  be 
so  mounted  on  a  pivot  such  as  L  (Fig. 
276)  that  it  will  always  line  up  with  the 
lever  pivot  as  the  lever  swings.  If  the 
rod  is  connected  through  a  spring  (Fig.  277),  or  if  the  piston 
is  designed  as  shown  in  Fig.  288,  the  cylinder  may  be  rigidly 
mounted. 

NOTE. — THE  SIZE  OF  DASH-POT  REQUIRED  FOR  A  GOVERNOR  varies 
with  the  load  conditions.  Ten  square  inches  per  100  engine  horse 
power  is  ordinarily  ample  where  the  dash-pot  stroke  is  about  equal  to  its 
bore.  Common  machine  oil  is  usually  used  in  dash  pots.  It  may  be 


''Mounting 
Lug 

FIG.  276.  —  Dash-pot  ad- 
justable by  valve,  V,  on 
outside. 


212     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 

thinned  with  kerosine  if  too  thick.     Cylinder  oil  or  glycerine  may  be 
used  if  a  thicker  liquid  is  required. 


Spring 

Dash-Pof 

Connection 


Motor- Contra/ fed 
Counterpoise-, 

P 


_  -Rocker-Arm  and  Rods  for 
'    Osc/J 'Idling  Knock-Off  Cams 


FIG.  277. — Nordberg  governor  showing  spring-connected  dash-pot  rod.  (If  the  safety 
idler,  I,  drops  due  to  failure  of  the  belt,  the  weights,  W,  will  be  released  and  the  pivot,  C, 
will  be  dropped.  This  will  operate  the  rods,  R,  S  and  T,  so  as  to  stop  the  engine.  When 
the  engine  is  driving  an  a.c.  generator,  the  motor,  M,  is,  when  synchronizing  the 
generator  with  another  generator,  so  controlled  by  the  operator  at  the  electrical  switch- 
board that  the  weight,  P,  is  shifted  to  such  a  position  that  the  engine  speed  is  changed  to 
the  proper  one  to  permit  synchronizing.  After  the  machines  have  been  synchronized, 
the  load  may  be  properly  divided  between  the  two  engines  by  the  operation  of  M. 

231.  Governors  May  Be  Adjusted  To  Change  Engine 
Speed  In  Several  Ways. — (1)  Weight  may  be  added  or  removed. 
Provision  is  often  made  for  adding  or  removing  weight 
(Figs.  277,  278  and  279).  A  weight  may  sometimes  be 
adjusted  in  or  out  on  a  lever  arm  (W,  Fig.  280).  Increasing 


SEC.  231]      FLY-BALL  STEAM-ENGINE  GOVERNORS 


213 


Shot  For 
Varying 
Weigh  t  Of 
Loact-- 


HoIeFor 
Putting  In 
Shot 


Hole  For 
Removing 
Shot-. 


the  leverage  or  the  weight,  where  the  weight  opposes  the  rise  of 
the  governor,  increases  the  engine  and  governor  speed  and 
vice  versa.  To  compute  even  approximately  the  amount  of 
weight  which  should  be  added  or  deducted  in  any  given  case 
usually  involves  complicated  calculations  and  a  knowledge 
of  the  weights  of  each  of  the  moving  parts  of  the  governor; 
see  note  under  Sec.  227.  Hence, 
in  practice,  the  most  direct 
method  of  finding  the  necessary 
amount  of  weight  is  by  trial.  (2) 
Increasing  or  decreasing  spring 
tension  or  adding  an  extra  spring 
changes  the  engine  speed.  Most 
spring-loaded  governors  (Figs. 
254,  265  and  273)  have  adjust- 
ments for  this  purpose.  When 
they  do  not,  an  extra  spring  (Fig. 
281)  may  be  added.  Increasing 
the  spring  tension  increases  en- 
gine speed.  (3)  A  take-up  adjust- 
ment may  be  provided  in  the 
governor  mechanism  (Figs.  282 
and  283).  Increasing  the  effec- 
tive length  of  the  linkage  in  such 
adjustments  ordinarily  decreases 
the  engine  speed.  In  increasing 
the  engine  speed  by  this  method 
when  a  Corliss  governor  is  used, 
make  sure  that  the  governor 
will  shut  off  completely  after  the  adjustment  is  made. 
The  collar  on  the  governor  spindle  may  have  to  be  raised 
to  permit  this.  It  is  dangerous  to  make  the  cut-off  later 
for  a  given  governor  position  without  testing  afterward  to 
make  sure  the  governor  will  shut  off.  (4)  Increasing  the 
weight  of  the  balls  of  a  loaded  governor  decreases  the  engine 
speed.  (5)  The  pulley  or  gear  sizes  may  be  changed  to  drive  the 
governor  at  a  different  speed  relative  to  the  engine  speed. 
That  is,  the  governor  continues  to  rotate  at  its  original 
speed  but  the  engine  speed  is  either  increased  or  decreased. 


Starting 
Lever-' 


FIG.  278. — Governor  which  may  be 
adjusted  for  different  speeds  by  adding 
or  removing  weight  (shot).  (Murray 
Iron  Works  Co.,  Burlington,  Iowa.) 


214     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE      [Div.  G 


Counterpoise 
Weight  May 
Be  Increased 
With  Shot--. 


Removable 
Weight  For 
Speed 
Adjustment 


FIG.  279. — General  arrangement  of  high-speed  loaded  Watt  governor  No.  2.     (Viller 
Mfg.  Co.,  Milwaukee,  Wis.) 


SEC.  231]      FLY-BALL  STEAM-ENGINE  GOVERNORS 


215 


If  the  governor  driving  pulley  —  on  the  engine  shaft  —  is  increased 
in  size,  the  engine  speed  will  be  proportionally  decreased.    If 


Sleeve. 


Increases  Speed 
in  This  Posit/on* 


E-Side  View 


FIG.  280. — Showing  weight  which  may  be 
adjusted  on  lever  to  change  the  engine  speed 
which  is  maintained  by  the  governor. 


'V//////////////////////// 

FIG.  281. — Extra  spring  added 
to  vary  the  governed  speed  of  an 
engine. 


FIG.  282. — Showing  speed  adjustment  provided  in  governor  linkage. 

the  driven  pulley  or  gear  is  increased  in  size,  the  speed  of  the 
engine  will  be  proportionally  increased  and  vice  versa. 


216     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 


Operaf/na 
Spindle-- 
Does  Not 
Revolve 


Guide 
'Spind/e 
'Stationary) 


NOTE. — THE  SENSITIVENESS  OF  A  GOVERNOR  Is  OFTEN  CHANGED 
ALSO  WHEN  THE  SPEED  Is  CHANGED.     Increasing  the  weight  or  spring 

tension  has  a  tendency  to  make 
the  governor  more  sensitive. 
Many .  paper-mill  engine  governors 
are  provided  with  double  cone 
pulley  drives  so  that  the  engine 
speed  may  be  increased  to  4  or 
5  times  the  minimum  speed  by 
shifting  the  drive  on  the  cones. 
Engines  equipped  with  such  gov- 
ernors are  called  variable  speed 
engines. 

NOTE. — THE  SPEED  AT  WHICH 
ENGINE  GOVERNORS  SHOULD  OP- 
ERATE Is  SOMETIMES  STAMPED  ON 
THE  GOVERNORS  by  the  manufac- 
turer of  the  engine.  If  it  is  not  so 
stamped  the  correct  operating 
speed  should  be  ascertained  from 
the  manufacturer  or  by  test  be- 
fore one  attempts  to  change  the 
engine  speed. 

EXAMPLE  . — An  engine  (Fig. 
284-7)  which  has  a  governor- 
driving  pulley,  P,  9  in.  in  diameter 
and  a  driven  pulley,  D,  12  in.  in 
diameter  is  operating  satisfactorily 
at  75  r.p.m.  What  change  should 
be  made  in  the  governor  drive  so 
that  the  engine  will  operate  at  65 
r.p.m.? 

SOLUTION. — For  satisfactory  op- 
eration, the  governor  should  oper- 
ate at  the  same  speed — the  same 
r.p.m.  of  the  governor  and  its 
pulley — as  before.  With  the  en- 
gine speed  decreased,  the  same 
governor  speed  may  be  maintained 
by  changing  either  pulley  P  or 
pulley  D;  or  by  changing  both 
pulleys  P  and  D,  and  using  new 
ones  of  properly  selected  diam- 
eters. If  pulley  P  is  changed,  its  new  diameter  should  be  9  X  75  -5- 
65  =  10.3  in.  If  pulley  D  is  changed,  the  diameter  for  a  65-r.p.m.  engine 
speed  should  be  12  X  65  •*•  75  =  10.4  in.  as  shown  in  Fig.  284-77. 
With  the  decrease  in  engine  speed,  there  will  have  to  be  a  very  slight 


FIG.  283. — Vertical  section  of  Pickering  gov 
ernor  showing  methods  of  adjustment. 


SEC.  231]      FLY-BALL  STEAM-ENGINE  GOVERNORS 


217 


decrease  in  the  valve  opening  to  maintain  the  lower  speed,  but  this  change 
in  valve  opening  may,  usually,  be  effected  by  an  adjustment  in  the 


Link~\ 


Counterpoise 


Governor- . 


.Governor  Driving 
p    /  Pulley;  9"Diam. 
,-•  Engine  Shaft 


/TT/////////////////////////////////////////////////'//////^////////'///// 
I-Old  Drive    (Engine  Speed  75  r.p.m.)          *~~Adjustable 

.Weight 


D/'am. 


10.4  D/am.~.J    Q 


fl-New    Drive  (Engine  Speed  65r.p.m.) 
FIG.  284. — Example — changing  governor-drive  pulleys  for  a  new  engine-speed. 

governor  linkage.     With  the  engine  speed  increased,  the  procedure  would 
be  the  reverse  of  that  just  described. 


JJ  Teeth^ 


•Governor 


75  Teeth.. 


36  Teeth. 


JO* )  ^wv^"  Shaft- 

I-New  Gearing 

.-Bevel  '     5/7,v/-  ^ 

u''  (Je^rj         .Governor- Drive  Gears'^/* 

Shaff  72  Teeth -^f: 


n-Old    Gearing 


Miter 
Gears-- 


FIG.     285. — Example — changing  either  spur-  or  bevel-gear  sizes  for  new  engine-speed. 

EXAMPLE. — If  the  governor  in  the  preceding  example  had  been  gear 
driven  (Fig.  285),  the  change  in  speed  might  have  been  made  by  changing 


218    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE      [Div.  6 

either  the  bevel  gears,  E  and  F,  or  the  straight  spur  gears,  A  and  B.  In 
either  case,  assuming  that  the  distance  between  the  meshing  gear  centers 
must  remain  fixed,  the  two  gears  which  mesh  must  both  be  changed. 
Assume  that  the  gears,  A  and  B,  are  4  diametral  pitch  (that  is,  4  teeth  per 
inch  of  diameter)  and  have  36  and  72  teeth  respectively.  The  pitch 
diameter  of  A  is  then  9  in.  and  that  of  B  18  in.  The  distance  between 
centers  must  remain  the  same  since  the  crank  shaft  and  pinion  shaft  are 
both  fixed.  This  distance  is,  in  this  case,  (9  -5-  2)  +  (18  -f-  2)  =  13.5  in. 
But  for  the  change  in  speed  required,  the  ratio  must  be  changed  in  the 
proportion  of  75  to  65  or  it  must  now  be  2  X  75  -5-  65  =  2.301.  If  the 
same  pitch  is  to  be  used,  the  total  number  of  teeth  in  both  gears  must 
remain  the  same  (108  teeth).  The  requirements  for  the  new  gears  are 
then  expressed  by  the  equations: 

M 

-ft-  =  2.301  and  M  +  N  =  108 

Where  M  is  the  number  of  teeth  in  the  new  pulley,  B',  and  N  is  the 
number  of  teeth  in  the  new  pulley  A' '.  Solving,  by  the  simultaneous 
equation  method,  M  =  75.3  and  N  =  32.7.  Taking  the  nearest  whole 
number  of  teeth  which  will  give  the  required  pitch  diameters,  there 
results :  33  and  75  for  the  required  number  of  teeth.  If  the  change  is  to 
be  made  in  the  bevel  gears,  a  new  pair  must  be  designed  or  selected  which 
will  provide  the  desired  ratio  and  Jhe  proper  shaft  alignments. 

EXAMPLE. — Certain  of  the  other  means  described  in  the  above  section 
for  changing  the  speed  of  the  engine  of  Fig.  284  are:  (1)  //  the  counter- 
poise, C,  is  made  lighter  it  will  decrease  the  speed  of  both  the  engine 
and  governor;  if  it  is  made  heavier,  it  will  increase  the  speed  of  both 
engine  and  governor.  (2)  Changing  the  weight  W  has  the  same  effect 
as  changing  C  because  the  rod  which  supports  W  is  connected  to  the 
spindle  which  carries  C.  Changing  the  weight,  W,  provides  a  convenient 
method  of  temporarily  changing  the  speed  of  the  engine.  Thus,  if  a 
machine  is  being  started  which  requires  considerable  power  and  which 
would  normally  slow  down  the  overloaded  engine,  a  weight  of  sufficient 
amount  may  be  added  to  W  to  maintain,  for  the  time  being,  the  engine 
speed  constant.  Then,  when  the  load  of  the  machine  is  discontinued,  the 
extra  weight  may  be  removed  from  W.  This,  as  compared  with  the 
modern  speed  regulating  devices  is  a  crude  expedient;  but  in  emergencies 
it  may  prove  serviceable.  (3)  //  the  weight,  D,  is  shifted  backward  or 
forward  on  its  lever,  it  will  change  slightly  the  speed  of  the  engine. 
(4)  Some  governors  have  at  L  a  link  of  adjustable  length  whereby  the  engine 
speed  may  be  changed;  see  "Caution"  below.  (5)  The  effective  length 
of  the  cam  rod,  R,  may  be  increased  or  decreased  to  change  the  engine  speed. 
Caution:  But  neither  this  plan  nor  the  one  just  preceding  it  should, 
ordinarily,  be  adopted.  Changes  in  L  may  affect  the  sensitiveness  of  the 
governor  mechanism.  Careless  adjustment  of  either  L  or  R  may  prevent 
the  realization  of  a  very  short  cut-off  and  thereby  cause  trouble — racing — 
if  all  of  the  engine's  load  is  suddenly  thrown  off. 


SEC.  232]      FLY-BALL  STEAM-ENGINE  GOVERNORS 


219 


232.  Governors  May  Be  Adjusted  For  Greater  Or  Less 
Speed  Regulation  but  such  adjustments  should,  whenever 
possible,  be  referred  to  the  manufacturer.  The  inexperienced 
engineer  is  cautioned  against  making  radical  adjustments  of 
this  sort.  (1)  Weight-loaded  governors  will  give  closer 
regulation  if  their  speed  is  increased  and  enough  dead  weight 
added  to  bring  the  engine  speed  back  to  its  original  value. 
Conversely,  if  the  speed  is  decreased  and  the  dead  weight 
lessened,  there  will  be  more  variation  in  speed.  (2)  If  a  weaker 
spring  is  substituted  in  a  spring-loaded  governor  and  this 


'I       H-rH  ..-Hanctwheet 
Various 
Holes  for 

Connecting  Governor 
Drop  Rod 

FIG.  286. — Showing  adjustable  governor  levers.  (Lever,  J,  is  adjusted  by  changing 
the  rod  pivot  from  one  hole  to  another.  Lever  //  is  adjusted  by  means  of  a  hand  wheel, 
H,  and  lead  screw,  L.) 

spring  is  compressed  more  so  as  to  exert  the  same  force,  the 
regulation  will  be  closer  because  a  lesser  change  in  pressure 
in  the  spring  will  then  be  required  to  produce  the  same  amount 
of  movement.  (3)  The  radius  of  a  governor  lever  (Fig.  286) 
may  be  so  adjusted  that  the  same  valve  movement  is  accom- 
plished with  less  governor  movement. 

NOTE. — AFTER  MAKING  ANY  OF  THE  ABOVE  ADJUSTMENTS  FOR 
CLOSER  SPEED  REGULATION,  there  may  be  trouble  with  the  governor 
hunting  and  the  dash-pot  resistance  may  have  to  be  increased  and  per- 
haps a  spring  inserted  in  the  dash-pot  rod  (Fig.  277)  mechanism. 

233.  Some  Governors  May  Be  Adjusted  For  Greater  Or 
Less  Promptness,  but  these  adjustments  should  ordinarily 


220    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 

be  left  to  the  governor  designer  and  manufacturer.  (1) 
Inertia  effect  may  be  introduced  to  secure  quicker  response 
but  such  a  change  ordinarily  requires  complete  re-design  of 
the  governor.  (2)  Spring  load  may  sometimes  be  substituted 
for  part  of  the  weight  load  in  a  weight-loaded  governor. 
The  spring  is  lighter  and  may  change  position  more  quickly 
than  a  weight.  (3)  A  spring  may  sometimes,  if  not  already 
used,  be  inserted  in  the  dash-pot  rod  (Fig.  277).  This  spring 
allows  the  governor  to  assume  its  new  position  at  once  and 


•Piston 
Rod 


Sleeve 


Support 

For 

,  -  Drop  Rod  End 

From  Governor     Of 

Chain 
U-Governor 
Co/umn  4- 


Valve 
Control  Rods 


FIG.  287. — Chain  recommended  as  substi- 
tute for  the  dash-pot  for  greater  promptness. 
(C.  E.  Bascom  in  Power,  June  29,  1915.) 


"Piston  Curved  To 
Prevent  B/nd/ng 

FIG.  288. — Spring  inserted  in 
dash-pot  to  retard  the  governor 
movement  near  the  no-load  po- 
sition. Caution:  If  this  device 
is  used,  the  engine  must  be 
watched  to  insure  that  it  will 
not  race  at  light  loads. 


the  dash-pot  adjusts  itself  later.  (4)  A  hanging  chain  (Fig. 
287)  has  been  recommended  as  a  substitute  for  a  dash-pot 
where  greater  promptness  is  desired.  (5)  A  lighter  oil  or 
larger  opening  in  the  dash-pot  gives  greater  promptness. 
A  heavier  oil  or  smaller  opening  in  the  dash-pot  gives  slower 
action — less  promptness.  (6)  A  spring  may  be  inserted  in 
the  dash-pot,  as  shown  in  Fig.  288,  if  the  engine  is  too  prompt 
near  no  load. 


SEC.  234]     FLY-BALL  STEAM-ENGINE  GOVERNORS 


221 


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222    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 

235.  Governors  May,  If  Incorrectly  Applied  Or  In  Poor 
Condition,  Allow  Engines  To  Race  for  various  reasons.  By 
"racing"  is  meant  the  accidental  running  of  an  engine  at 
considerably  above  the  speed  for  which  it  was  designed. 
(The  following  material  is  based  partly  on  W.  Trinks,  GOVER- 
NORS AND  THE  GOVERNING  OF  PRIME  MOVERS.)  (1)  //  the 
racing  takes  place  with  an  old  governor  which  has  given  several 
months  or  years  of  satisfactory  service,  the  chief  causes  are: 

(a)  The  dash-pot  may  be  in  poor  condition  or  poorly  adjusted.  Air 
pockets  in  the  dash-pot  are  likely  to  cause  racing.  If  the  oil  opening  in 
the  piston  or  valve  is  too  large,  too  sudden  variation  in  governor  position 
may  be  allowed.  Under  these  conditions  either  the  opening  should  be 
partly  closed  or  a  heavier  oil  used. 

(6)  The  valves  may  have  been  adjusted  so  that  the  governor  no  longer 
properly  controls  them.  If  adjustments  have  been  made  in  the  valves, 
the  governor  linkage  may  have  to  be  adjusted  also.  Racing  from  this 
cause  usually  occurs  only  at  light  loads,  and  is  prevented  by  adjusting 
the  governor  linkage  so  that  the  valves  may  shut  off  completely  at  no 
load. 

(c)  There  may  be  excessive  friction  somewhere  in  the  mechanism. 
Such  friction  may  usually  be  detected  by  moving  the  governor  by  hand 
either  directly  or  with  a  bar,  care  being  taken  not  to  strain  the  apparatus. 
It  may  be  caused  by  the  framework  of  the  governor  becoming  twisted  out 
of  line,  in  throttling  governors  by  poor  oil  or  dirt  clogging  the  valve,  or 
a  number  of  other  causes. 

(d)  The  Corliss  releasing  gear  controlled  by  the  governor  may  be  in 
poor  condition.     The  knife  edges  may  be  so  dulled  that  they  slip  and  are 
uncertain  in  their  action.     The  dash-pot  of  the  valve  may  not  close  it 
completely  when  released.     This  latter  trouble  may  be  remedied  tempo- 
rarily by  tying  a  long  flexible  spring  to  the  dash-pot  arm  to  assist  the  dash- 
pot  in  closing  the  valve.     This,  of  course,  is  a  makeshift  and  the  dash-pot 
should  be  repaired  as  soon  as  possible. 

(e)  Where  the  governor  is  belt-driven,  the  belt  may  be  slipping  at 
times.     Pressing  down  on  the  idler,  or  using  a  belt  tightner,  will  indicate 
whether  or  not  this  is  the  trouble.     When  this  occurs,  either  the  belt  is 
too  loose  or  oily,  or  there  is  undue  friction  in  the  governor  spindle  bearings 
or  gears. 

(/)  If  the  governor  has  been  adjusted  for  a  considerable  change  in 
speed,  it  may  have  been  made  unstable  by  the  adjustment.  It  may  be 
made  more  stable  as  indicated  in  Sees.  232  and  234,  by  adjusting  for 
greater  speed  regulation. 

(2)  //  the  racing  occurs  with  a  new  governor  which  has  never 
given  any  satisfactory  service,  the  trouble  should,  whenever 
possible,  be  referred  to  the  manufacturer  New  governors  are 


SEC.  236]      FLY-BALL  STEAM-ENGINE  GOVERNORS 


223 


Governor 
Co/umn  - 


Segment 

Or&duated  To 
Read 
Load 

i  On 
Engine 


likely  to  be  improperly  adjusted  to  the  load  conditions  (see 
Sees.  231  to  234).  Racing  of  a  new  governor  may  be  due  to 
any  of  the  causes  given  under  old  governors.  In  addition, 
there  may  be  errors  in  the  design  or  defects  in  the  manufacture. 
Errors  in  design  can  sometimes  be  corrected  by  placing  a  spring 
in  the  dash-pot  (Fig.  288)  so  that  it  will  come  into  play  in  some 
particular  position  in  which  the  governor  does  not  behave 
properly. 

NOTE. — MOST  OF  THE  TROUBLES  WHICH  CAUSE  RACING  ALSO  CAUSE 
SLACKING  UP  UNDERLOAD — that  is,  failure  of  the  governor  to  increase  the 
steam  supply  to  meet  increased  load. 

NOTE. — The  proper  adjustments  of  the  Corliss  engine  governor 
mechanism  are  given  in  detail  in  Sec.  192. 

236.  The  Principal  Causes  Of  A  Governor's  Lagging  Too  Far 
Behind  The  Engine  During  Changes  In  Load  are:  (1)  The 
governor  is  too  small  or  is  not  of 

a  sufficiently  prompt  type  for  the 
load  conditions.  (2)  The  damp- 
ing or  retarding  action  of  the 
dash-pot  is  too  great.  (3)  The 
movement  provided  by  the  gov- 
ernor proper  may  be  too  small  to 
operate  the  governing  valve.  (4) 
There  may  be  friction  in  the 
mechanism  which  is  slowly  re- 
lieved by  the  vibration. 

NOTE. — An  adjustment  for  greater 
promptness  (Sec.  233)  will  often  re- 
medy troubles  (1),  (2)  and  (3)  above. 

237.  If  The  Governor  Vibrates 
(Dances  Or  Jerks),  The  Causes 
Of  The  Trouble  may  be:  (1)  The 
governor   is   too   light,   a  more 
massive  one  should  be  used.     (2) 
The  damping  action  of  the  dash- 
pot  is  not  sufficient.     (3)  The  mechanism  is  mechanically  poor 
and  needs  repair.     (4)  The  belt  may  be  poorly  spliced  so  that 
the  governor  jumps  as  the  splice  goes  over  the  pulley.     A 
"load  indicator"  (Fig.  289)  helps  detect  troubles  of  this  sort. 


FIG.  289. — Homemade  load  indicator 
for  engine  governors.  (The  indicator 
hand,  /,  and  segment,  S,  are  made  of 
wood  or  tin  and  installed,  as  shown, 
with  an  adjustable  rod,  R,  and  pins  or 
bolts.  The  segment  when  marked 
correctly,  shows  at  a  glance,  the  load 
which  the  engine  is  delivering.  It  also 
assists  in  detecting  "hunting"  and 
jerking  of  the  governor.) 


224    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 


NOTE. — HEATING,  WEAR,  POOR  ALIGNMENT,  WOBBLING,  BUCKLING, 
etc.,  are  likely  to  affect  governor  operation,  just  as  they  would  that  of  any 
other  mechanical  device.  Close  adjustment  and  good  action  are  not 
always  possible  where  troubles  of  this  sort  are  present.  Another  point  to 
remember  is  that  good  governing  is  usually  impossible  when  the  engine 
valves  are  in  poor  condition. 

238.  In   Ordering  A  Throttling   Governor,   the   following 
questions  should  be  answered  (based  on  Pickering  and  Gardner 
governor  catalogues):  (1)  What  type  or  catalogue  number  is 
preferred?     (2)    Is  the   engine   vertical   or   horizontal?     (3) 
Diameter  of  engine  piston?     (4)  Length  of  piston  stroke? 
(5)  What  is  the  lowest  speed  required  of  the  engine?     (6) 
What  is  the  highest  speed  required  of  the  engine?     (7)  What 
is  the  class  of  service  for  which  the  engine  is  used?     (8)  Inside 
diameter  and  length  of  steam  pipe  ?     (9)  Diameter  of  governor- 
driving  pulley  on  engine  shaft?     (10)  Width  of  belt  driving 
governor?     (11)  What  steam  pressure  is  ordinarily  carried? 
(12)  Degree  of  superheat  if  any?     (13)  Is  the  flywheel  on  the 
engine  large  enough  to  keep  the  engine  speed  steady  at  all  times? 

239.  The  Following  Table  Gives  The  Sizes  Of  Throttling 
Governors    ordinarily    required   (Jarecki  Mfg.  Co. — "Erie" 
governor) : 


Engine  cylinder  diameters,  inches 

Governor  size, 

diameter  of 
opening, 

Piston  speeds,  feet  per  minute 

inches 

300 

400 

500 

600 

1H 

7 

6 

5 

m 

2'; 

9 

8 

7 

6 

2K 

12 

10 

9 

8 

3 

14 

12 

10 

9 

3^ 

16 

14 

12 

11 

4 

18 

16 

14 

S3 

4^ 

20 

18 

16 

15 

5 

22 

20 

18 

16 

6 

26 

23 

21 

19 

7 

31 

27 

24 

22 

8 

36 

31 

28 

25 

9 

40 

35 

31 

28 

10 

45 

39 

35 

32 

SEC.  240]      FLY-BALL  STEAM-ENGINE  GOVERNORS 


225 


240.  A  Governor  Once  In  Good  Condition  Requires  The 
Following  Attention. — Keep  the  governor  clean  and  see  that 
all  oil  holes  are  kept  free.  Use  good  oil.  Pack  valve-stem 
stuffing  boxes  of  throttling  governors  with  candle-wicking 
packing  of  good  quality  soaked  in  oil.  Remove  all  old 
packing  when  re-packing.  See  that  the  valve  stem  is  smooth 
and  clean.  Tighten  the  gland  just  enough  to  prevent  escape 
of  steam.  For  repair  of  governor  valves  see  the  author's 
STEAM  POWER  PLANT  AUXILIARIES  AND  ACCESSORIES.  Some 
engineers  advise  allowing  a  little  steam  to  escape  around  the 


Lock 
Nut-'' 

Ac/justing  ^ 
Screw-' 

FIG.  290. — Showing  adjustable  thrust  bearing  for  fly-ball  governors. 

stem  to  keep  the  packing  lubricated  and  soft;  and  advise  re- 
packing every  30  days.  Changes  in  speed  should,  ordinarily, 
be  made  by  methods  recommended  by  the  manufacturer. 
Belts  must  be  tightened  occasionally.  Ball  bearings  (Fig. 
278)  must  sometimes  be  renewed.  Knife  edges  on  sensi- 
tive governors  (Fig.  273)  will  sometimes  have  to  be  sharpened. 
Thrust  bearings  (Fig.  290)  occasionally  need  to  be  adjusted 
to  make  the  gears  mesh  properly. 

241.  Compound  Engines  May  Be  Governed:  (1)  By 
governing  the  high-pressure  cylinder  only.  (2)  By  governing 
both  cylinders.  The  first  method  is  used  largely  with  small 

15 


226    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  6 

engines  and  engines  which  are  working  under  very  steady 
loads.  The  cut-off  of  the  low-pressure  cylinder  is  then  fixed 
at  a  point  which  will  give  a  proper  receiver  pressure  under  the 
load  expected.  The  objection  to  this  method  of  governing 
is  that  it  is  too  slow  under  most  conditions  since  the  changes 
in  load  are  not  compensated  for  in  the  low-pressure  cylinder 
until  the  receiver  pressure  has  changed.  This  change  may 
require  several  strokes  of  the  engine.  It  is  an  economical 
method  of  governing  when  it  is  applicable.  When  the  second 
method  is  used,  a  mechanical  connection  is  ordinarily  made 
between  the  valve  gears  of  the  two  cylinders  so  that  a  move- 
ment of  the  governor  changes  the  cut-off  on  both  cylinders 
proportionally.  See  Div.  8  for  a  further  discussion  of  com- 
pound-engine governing. 

QUESTIONS  ON  DIVISION  6 

1.  Why  is  a  steam-engine  governor  usually  necessary?     When  is  one  unnecessary? 

2.  Why  does  not  a  governor  keep  the  engine  speed  exactly  constant  ?     What  variations 
in  engine  speed  do  governors  in  practice  permit? 

3.  What  two  forces  are  utilized  by  governors  in  detecting  speed  variations?     Which  is 
employed  principally  in  fly-ball  governors? 

4.  What  two  methods  do  fly-ball  governors  use  for  controlling  the  steam  supply  to  the 
engine?     Which  gives  the  best  engine  performance?     Why? 

5    Show  by  a  sketch  one  safety  feature  often  used  in  throttling  governors.     One  used 
in  Corliss  governors.     What  disaster  may  occur  if  the  governor  fails? 

6.  How  should  governor  belts  be  spliced?     Show  by  a  sketch  some  extra  fastenings 
which  may  be  used  on  governor  pulleys  and  levers. 

7.  Give  some  precautions  which  should  be  taken  to  lessen  the  danger  of  governor 
failure. 

8.  What  is  meant  by  a  sensitive  governor?     One  with  small  coefficient  of  regulation? 
A  prompt  governor?     A  sluggish  governor?     A  powerful  governer? 

9.  How  are  tests  for  speed  regulation  usually  made?     What  bad  effect  results  from 
momentary  variation  in  speed  of  an  engine  driving  a  lighting  generator? 

10.  Give  four  advantages  of  a  loaded  governor  over  a  simple  pendulum  governor. 

11.  What  is  meant  by  a  stable  governor?     An  isochronous  governor?     Why  cannot 
neutral  and  unstable  governors  be  used  in  engineering? 

12.  On  what  does  the  centrifugal  force  in  a  revolving  weight  depend? 

13.  Explain  by  a  sketch  how  balls  hung  from  different  length  arms  rise  to  the  same 
height  when  revolved  at  the  same  speed. 

14.  State  some  relations  between  forces,  weights  and  speeds  in  fly-ball  governors. 

15.  What  advantage  has  a  spring-loaded  governor  over  a  weight-loaded  one? 

16.  Explain  with  a  graph  the  hunting  of  a  governor  after  a  sudden  change  in  load. 

17.  What  difference  is  there  in  the  effect  of  fluid  friction  and  mechanical  friction  on 
governor  operation?     What  liquids  are  frequently  used  in  dash-pots? 

18.  Describe  the  action  of  an  adjustable  dash-pot. 

19.  Name  four  methods  of  adjusting  governors  for  different  engine  speeds.     What 
speed  adjustment  (Table  234)  has  no  other  effect?     How  may  a  governor  be  adjusted  for 
less  speed  regulation? 

20.  What  is  the  danger  of  adjusting  a  governor  for  too  little  speed  regulation? 

21.  How  may  a  governor  be  adjusted  for  greater  or  less  promptness? 


SEC.  241]      FLY-BALL  STEAM-ENGINE  GOVERNORS  227 

22.  Give  some  of  the  principal  causes  of  racing  and  their  remedies. 

23.  What  will  cause  a  governor  to  respond  too  slowly  to  a  change  in  load  on  the  engine? 
By  what  general  method  may  this  be  overcome? 

24.  What  will  cause  a  governor  to  vibrate? 

25.  Name  thirteen  points  of  information  which  should  be  given  in  ordering  a  throttling 
governor. 

26.  What  size  throttling  governor  is  required  for  an  engine  running  500  ft.  per  min. 
piston  speed,  having  a  bore  of  14  in.,  under  average  conditions? 

27.  What  care  does  a  governor  usually  require  after  it  has  once  been  put  in  good 
condition? 

28.  What  are  the  advantages  of  the  two  methods  of  governing  compound  engines? 

PROBLEMS  ON  DIVISION  6 

1.  What  is  the  coefficient  of  regulation  of  a  governor  if  the  engine  runs  201  r.p.m.  at  no 
load  and  197  r.p.m.  at  full  load? 

2.  To  what  height  from  the  upper  pivot  will  the  balls  of  a  simple  pendulum  governor 
rise  at  87  r.p.m.? 

3.  What  centrifugal  force  will  be  developed  in  a  governor  ball  weighing  6.25  Ib.  revolv- 
ing at  500  r.p.m.  at  a  radius  of  4.32  in.? 

4.  A  governor  makes  3.7  revolutions  for  each  revolution  of  the  engine,  the  engine 
running  at  105  r.p.m.     How  many  revolutions  should  the  governor  make  per  revolution 
of  the  engine  if  the  governor  is  to  be  adjusted  by  changing  the  pulley  sizes  to  allow  the 
engine  to  run  at  125  r.p.m.     If  the  adjustment  is  to  be  made  by  changing  the  governor- 
driving  pulley  on  the  crank  shaft,  which  was  previously  14  in.  in  diameter,  what  size 
pulley  should  be  substituted? 

5.  The  counterpoise  on  a  Porter  governor  weighs  145  Ib.  and  the  weights  12  Ib.  each 
If  the  height  from  the  center  of  the  ball  to  the  intersection  of  the  arm  and  spindle  axes  is 
16  in.  in  starting  position,  at  what  speed  will  the  governor  lift? 


DIVISION  7 

SHAFT    STEAM-ENGINE     GOVERNORS,    PRINCIPLES 
AND  ADJUSTMENTS 

242.  A    Shaft    Steam-Engine    Governor    Is    One    Which 
Revolves  About  The  Engine  Crank  Shaft  As  A  Center. — A 

shaft  governor  is  (Fig.  291)  commonly  located  in  the  flywheel 
of  the  engine  and  governs  the  engine,  as  will  be  explained 
later,  by  changing  the  position  of  the  eccentric  or  the  valve- 
operating  crank.  Shaft  governors  are  widely  used  on  medium 
and  high-speed  engines  (150  to  400  r.p.m.  depending  on  the 
size;  see  also  Sees.  74  and  75)  of  the  slide-valve,  poppet- 

D/recfion  Of 
Rotation 


Valve-. 


FIG.  291. — Skinner  engine-governing  mechanism. 

valve  and  non-releasing  Corliss-valve  types  and  are  adapted 
to  service  where  sudden  large  changes  in  load  occur  and  where 
close  regulation  is  desired.  Single-valve  engines  which  are 
equipped  with  shaft  governors  are  often  called  automatic 
engines.  Shaft  governors  are  sometimes  called  automatic 
cut-off  governors. 

NOTE. — ALL  SHAFT  GOVERNORS  ARE  "VARIABLE  CUT-OFF"  GOVER- 
NORS.    Their  action  is  therefore  superior  to  that  of  throttling  governors 

228 


SEC.  243]         SHAFT  STEAM-ENGINE  GOVERNORS  229 

insofar  as  economy  is  concerned.  However,  a  shaft-governed  simple 
slide-valve  engine  does  not  show  as  good  an  economy  as  does  a  fly-ball- 
governed  Corliss-valve  engine.  Fig.  292  shows  the  governing  action  of 
the  Skinner  engine  governor  (Fig.  291).  The  line  A  corresponds  to  a 
little  more  than  friction  load;  the  line  B  to  about  normal  load;  and  the 
line  C  to  maximum  load.  It  will  be  noted  that  the  cut-off  is  less  sharp 
and  the  expansion  lines  less  regular  than  with  a  Corliss  gear  (Fig.  256). 
Also  there  is  more  throttling  at  light  loads  with  a  shaft-governor  cut-off 
gear  than  with  a  Corliss  releasing 
gear.  Furthermore,  the  compression 
line  is  changed  (Fig.  292)  with  the 
shaft  governed  engine  whereas  it  is 
not  changed  with  the  releasing  Corliss 
engine. 


243.  The  Fundamental  Prin- 


Atmospheric  Pressure-*    Back  Pressure-- 


ciples  And  Terms  Relating  To      Fm.  292._showing  the  eflect  of  vari. 

Fly-Ball      Governors       (DiV.      6)     able  cut-off  governing  by  a  shaft  gover- 

Apply  Also  To  Shaft  Governors.  nor-  (Cutoff  occurs  at  Zl-  *••  z«-> 
For  example,  shaft  governors  may  be  stable,  unstable,  may 
allow  racing,  may  hunt,  may  require  dash-pots  or  may  give 
too  much  speed  regulation  for  very  much  the  same  reasons 
as  were  explained  under  fly-ball  governors.  Shaft  governors, 
however,  do  not  permit  of  as  many  adjustments  as  do  fly-ball 
governors.  Shaft  governors  cannot  ordinarily  be  adjusted 
while  in  motion.  The  two  principal  methods  of  adjustment, 
as  will  be  explained,  are  varying  the  weights  and  varying 
the  spring  tension  (Sec.  255). 

NOTE. — THE  FORCES  REQUIRED  FOR  SHAFT  GOVERNING  are  ordinarily 
much  greater  than  those  required  for  governing  by  the  methods  explained 
in  Div.  6.  In  shaft  governing,  the  eccentric  must  be  held  by  the  governor 
in  a  certain  position  for  each  load — it  must  be  held  there  with  sufficient 
firmness  that  the  valve-gear  friction  will  not  displace  it.  This  necessi- 
tates the  exertion  of  a  relatively  considerable  force.  Also,  the  forces 
which  the  governor  must  exert  depend  on  the  valve  gear  and  its  reaction 
to  the  governor  and  eccentric  motion.  It  is  therefore  impossible  to 
exactly  analyze  the  forces  in  a  shaft  governor  by  considering  only  the 
governor  itself.  They  must  be  considered  in  connection  with  the  valve 
gear  which  the  governor  operates.  A  shaft  governor  must  be  specially 
designed  as  a  part  of  the  engine  on  which  it  is  to  operate. 

244.  Shaft  Governors  Employ  For  Their  Operation  Forces 
Of  Two  Kinds:  (1)  Centrifugal  force,  Sec.  213.  (2)  Inertia, 
Sec.  213.  In  this  respect  they  differ  from  fly-ball  governors 


230    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  7 


Flu- 

Whee! 


which  employ  centrifugal  force  only.  How  these  forces  are 
utilized  in  shaft-governor  operation  is  explained  in  the  succeed- 
ing sections. 

245.  Centrifugal  Force  Effects  The  Permanent  Control  In 
Shaft  Governors. — Fig.  293  illustrates  an  imaginary  shaft 
governor  which  employs  only  centrifugal  force  for  its  operation. 
In  all  shaft  governors  there  is  a  weight  (W,  Fig.  293)  supported 
by  an  arm  or  arranged  to  slide  in  guides,  G,  which  are  connected 

to  a  revolving  flywheel,  F,  so 
that  the  centrifugal  force  tends 
to  throw  the  weight  away  from 
the  center,  C,  of  the  wheel.  A 
spring,  S,  is  employed  to  count- 
eract the  effect  of  centrifugal 
force  and  is  so  arranged  as  to 
restore  the  weights  to  normal 
position  when  the  engine  comes 
to  rest.  In  the  governor  shown 
in  Fig.  293  the  centrifugal  force 
tends  to  throw  W  outward  and 
toward  the  circumference  of  the 
wheel,  whereas  the 
spring  tends  to  draw  W  inward. 
The  spring  thus  counteracts  the  centrifugal  force,  holding  the 
governor  in  such  position  as  to  maintain  an  almost  uniform 
speed. 

When  W  is  forced  in  toward  the  center  it  increases  the  eccen- 
tricity of  the  crank  pin  (Sec.  148)  and  when  it  is  forced  away 
from  the  center  it  decreases  the  eccentricity. 

NOTE. — By  properly  proportioning  and  arranging  the  weights  and  the 
spring,  it  is  possible  to  make  a  shaft  governor  of  this  centrifugal  class  so 
that  its  parts  will  move  directly  proportionally  to  any  change  in  speed  of 
the  engine.  But  for  reasons  given  in  Sec.  248  the  force  of  inertia  is  also 
employed  in  all  modern  commercial  shaft  governors. 

NOTE. — No  GOVERNOR  EMPLOYING  CENTRIFUGAL  FORCE  As  A  REGU- 
LATING MEANS  CAN  OPERATE  WITHOUT  SOME  CHANGE  IN  THE  ENGINE 
SPEED  As  THE  LOAD  ON  THE  ENGINE  CHANGES.  In  Div.  6,  it  was 
stated  that  no  change  in  governor  position  occurred  until  a  change  in 
speed  had  taken  place.  This  statement  is  equally  true  of  shaft  governors 
in  spite  of  certain  manufacturers'  claims  to  the  contrary.  However, 


FIG.  293. — Showing  imaginary  shaft 
governor  which  operates  by  centrifugal 
force  only.      (This  imaginary  construe-     rpvolvinff 
tion  is  never  used  in  actual  governors.) 


SEC.  246]         SHAFT  STEAM-ENGINE  GOVERNORS 


231 


Direction  Of 
'  Revo/ uf ion 


with  shaft  governors  the  difference  between  the  no-load  and  full-load 
speeds  may  be  less  than  one  revolution  in  300 — speed  regulation  of  ^  of 
1  per  cent.  Such  a  small  speed  variation  would  be  difficult  to  detect 
with  a  revolution  counter.  If  an  engine  is  operating  at  no  load  and  the 
load  is  suddenly  thrown  on,  the  engine  may,  due  to  the  inertia  effect  (see 
Sec.  213)  of  the  governor,  attain,  in  accelerating,  a  speed  greater  than  the 
no-load  speed  before  the  governor  reaches  equilibrium.  But  this  extra 
speed  is  only  temporary.  For  normal  operation,  the  engine  must  run 
a  little  slower  at  full  load  than  at  no  load. 

246.  Inertia  Forces  Effect  Temporary  Control  In  A  Shaft 
Governor. — The  principle  of  inertia  is  employed  in  shaft 
governors  for  preventing  sudden 
changes  in  speed  in  somewhat  the 
same  way  as  it  is  employed  in  fly- 
wheels. The  inertia  governor  may 
thus  be  considered  a  sort  of  auxiliary 
flywheel  which  acts  through  the 
valves  of  the  engine  instead  of 
acting  directly  on  the  crank  shaft. 
The  principle  of  inertia  is  one  of 
Sir  Isaac  Newton's  laws  of  mo- 
tion. It  may  be  stated — as  ap- 
plied to  revolving;  governor  parts 

FIG.  294.— Imaginary  shaft  gover- 
thUS :    A     body    at    rest    tends    tO     nor  which  would  be  affected  by  in- 

remain  at  rest;  and  when  revolv-  ertia  only-    (This  Construction  is 

never  used.) 

ing,    tends   to   continue   revolving 

at  a  uniform  speed.  Fig.  294  shows  an  imaginary  shaft 
governor  which  would  operate  by  inertia  only.  The  weighted 
bar,  WW,  is  pivoted  at  its  center  of  gravity,  G.  Since 
the  bar  is  so  pivoted,  it  has  no  tendency  to  revolve  on  its 
pivot  due  to  centrifugal  force.  It  is  held  loosely  in  place  by 
springs  and  kept  from  extreme  rotation  by  the  stops,  BB. 
Now,  if  the  flywheel,  F,  is  suddenly  started  in  the  direction 
indicated,  the  weighted  bar  will,  due  to  its  inertia,  tend  to 
"hang  back."  It  will  rotate,  relative  to  the  flywheel,  so  that 
the  valve-operating  crank  pin,  P,  will  be  brought  nearer  the 
center  of  the  shaft,  C,  which  is  equivalent  to  decreasing  the 
eccentricity,  Sec.  148.  This  movement  will  decrease  the  valve 
travel  and  the  speed  of  the  engine  will  thus  be  checked.  A 
governor  of  this  sort  would  prevent  sudden  changes  in  engine 


232    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  7 


Direction  Of 

( F/ywhee/  Rotation 


speed  but  it  would  allow  any  amount  of  gradual  engine-speed 
change.  Consequently,  for  a  shaft  governor  which  is  to 
maintain  some  definite  engine  speed,  centrifugal  force  (Sec. 
213)  must  also  be  employed. 

247.  A  Shaft  Governor  Secures  Prompt  Action  And  Close 
Regulation  By  Combining  Centrifugal  Force  And  Inertia. 
The  elementary  governor  bar,  IW,  of  Fig.  295  is  so  arranged 
that  its  mass  is  affected  by  both  centrifugal  force  and  inertia. 
The  governor  bar  is  pivoted  at  M  (not  at  its  center  of  gravity) 

and  carries  a  large  "  centrifu- 
gal" weight,  W,  and  a  smaller 
' '  inertia ' ;  weight,  I .  The  whole 
bar,  however,  is  acted  upon  by 
both  centrifugal  force  and  in- 
ertia. It  is  prevented  from 
rotating  excessively  by  the 
stops,  B.  The  center  of  gravity 
of  the  bar  is  at  G.  The  bar 
carries  also  the  valve-operating 
crank  pin,  P,  which  operates 
the  valves  of  the  engine  through 
the  valve  rod  and  valve  stem. 
Assume  that  the  flywheel  is 
being  started  in  the  direction 
of  arrow  R.  As  the  flywheel 
speed  increases,  the  center  of  gravity  tends  to  move  outward 
as  indicated  by  the  arrow  T,  but  is  restrained  by  the  spring. 
If  the  speed  of  the  flywheel  increases  suddenly,  the  weights, 
due  to  their  inertia,  tend  to  rotate  in  the  direction  indicated 
at  S,  against  the  spring  tension.  This  movement  will  bring 
the  pin,  P,  closer  to  the  center,  C,  and  the  travel  of  the  valve 
will  thus  be  reduced.  With  a  reduced  valve-travel,  the  engine 
will  be  unable  to  further  increase  its  speed.  After  the  speed 
becomes  uniform  at  its  higher  value,  the  weights  will  exert  no 
inertia  effect.  Inertia  will,  therefore,  no  longer  keep  the 
governor  in  its  new  position  but  an  increased  centrifugal  force 
will  then  have  been  developed  (Sec.  213)  due  to  the  increased 
speed.  This  force  will  maintain  the  governor  bar  in  the  new 
position.  If  the  speed  slackens,  the  above-described  processes 


FIG.  295. — Diagram  of  governor  of 
the  "Rites"  type.  (This  arrangement 
is  the  most  widely  used  of  any  shaft 
governor  arrangement  but  the  dis- 
tances shown  above  are  exaggerated.) 


SEC.  248]         SHAFT  STEAM-ENGINE  GOVERNORS  233 

will  be  reversed,  the  spring  operating,  after  the  speed  is 
uniform  and  inertia  is  no  longer  effective,  to  retain  the  bar  in 
its  low-speed  position.  The  hunting  of  a  shaft  governor  which 
actually  occurs  before  it  attains  its  final  condition  of  equilib- 
rium for  the  given  load  is  similar  to  that  described  for  fly- 
ball  governors  in  Sec.  229.  It  is  not  therefore  treated  in  this 
explanation. 

248.  Why  Shaft  Governors  Employ  Both  Centrifugal  Force 
And  Inertia  in  order  to  secure  prompt  action  may  be  explained 
as  follows:  A  shaft  governor,  due  to  the  considerable  force 
which  it  must  exert  to  keep  the  eccentric  in  position  against  the 
friction  of  the  valve  and  valve  gear,  must  be  relatively  heavy— 
that  is,  it  must  be  many  times  heavier  for  a  given  service  than 
a  fly-ball  governor.     As  explained  in  Div.  6,  a  governor  which 
is  very  heavy  is   correspondingly  slow  or  sluggish  if  only 
centrifugal  force  is  used.     Hence,  it  is  obvious  that,  with 
heavy  weight  arms,   to  insure  the  prompt  action  which  is 
essential  for  close  speed  regulation,  a  shaft  governor  must 
employ  some  force  other  than  centrifugal  force.     Hence  nearly 
all  shaft  governors  are  so  designed  that  the  inertia  of  the 
weights  will  assist  the  governor  in  changing  position.     By  thus 
employing  inertia,   a  shaft  governor  obtains  more  prompt 
action  than  is  ordinarily  possible  with  a  fly-ball  governor. 
The  speed  regulation  of  a  good  shaft  governor  is  within  less 
than  1  per  cent,  regardless  of  whether  the  change  in  load  is 
made  slowly  or  suddenly.     Furthermore  the  governing  action 
is  so  prompt  that  a  well-designed  shaft  governor  will  attain  its 
new  position  for  a  changed  load  within  1  or  2  revolutions,  which 
may  represent  but  a  fraction  of  a  second. 

249.  How  A  Shaft  Governor  Controls  The  Speed  Of  An 
Engine  may  be  understood  by  referring  to  Figs.  296,  297  and 
298.     The   governor   shown   is  arranged  to  vary  the  valve 
travel  without  changing  the  angular  advance  of  the  eccentric 
materially. 

EXPLANATION. — The  governor  is  shown  in  Fig.  296  in  full-load  position. 
The  valve-operating  crank-pin,  P,  which  is  carried  on  the  governor  bar, 
travels  in  a  large  circle,  E,  giving  a  maximum  valve  travel.  The  engine 
steam  port,  A,  has  therefore  a  large  opening  at  quarter  stroke  and 
cut-off  occurs  late.  If  the  load  is  suddenly  thrown  off  the  engine,  the 


234     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  7 

governor  will  assume  the  new  position  shown  in  Fig.  297,  explained  in 
Sec.  247,  and  the  crank  pin  then  travels  in  a  smaller  circle,  E'  (Fig.  297). 
The  travel  of  the  crank  pin  is  now  but  little  more  than  sufficient  to 

.  -  Direction  Of  Ro  tat  ion 

•  Governor 

Arm. 

j  Equal 
.  Arms. 


FIG.  296. — Method  of  governing  with  shaft  governor  and  slide  valve.     (Takes  steam  for 
nearly  full  stroke.) 


,' Direct  ion  Of  Rotation 

Governor 


-'  -Steam 
m  Supply 


FIG.  297. — Method  of  governing  with  shaft  governor  and  slide  valve.      (Cut-off  at 
about  one-fourth  stroke.) 


.-Direct/on  Of  Rotation 

Governor  Rocker 

^Arm  :''Arm 

?uaf 
rmsj 


Steam 


FIG.  298. — Method  of  governing  with  shaft  governor  and  slide  valve.     (Steam  cut  off 

entirely.) 

uncover  the  admission  port  at  A',  and  cut-off  occurs  a  little  past  quarter 
stroke.  Less  steam  will  now  be  admitted  to  the  engine  and  the  engine 
speed  will  be  prevented  from  further  increasing.  With  the  arrangement 


SEC.  250]         SHAFT  STEAM-ENGINE  GOVERNORS  235 

shown,  compression  occurs  earlier  in  Fig.  297  than  in  Fig.  296.  This  also 
helps  to  cause  the  engine  to  develop  less  power  if  the  governor  position  is 
changed  as  described  above.  The  extreme  position  of  the  governor  is 
shown  in  Fig.  298,  where  the  throw  of  the  eccentric  is  less  than  the 
steam  lap  of  the  valve  so  that  the  steam  is  shut  off  from  the  cylinder 
entirely. 

NOTE. — The  engine  shown  in  Figs.  296  to  298  runs  "under."  If 
the  governor  arm  and  spring  were  reversed  in  position  (turned  over  from 
left  to  right)  the  engine  would  run  "over." 

250.  Reversing  An  Automatic  Engine  should  be  avoided 
whenever    possible.     The    engine   has  probably  been  nicely 
adjusted  before  it  left  the  factory  and  it  is  usually  difficult 
for  the  inexperienced  person  to  re-adjust  the  wheel  correctly. 

NOTE. — To  REVERSE  A  TROY  AUTOMATIC  ENGINE,  do  not  disturb  the 
valve  nor  remove  the  flywheel  from  the  engine  shaft.  Remove  the 
governor  arm  (Fig.  299)  and  reverse  it  on  the  pin — turn  out  the  side 
which  was  against  the  wheel.  Then  re-key  it  to  the  pin  using  the  other  an- 
gle key- way  which  is  provided  in  the  pin.  The  stops,  drag  spring  and  coil 
spring  must  be  carefully  reversed  in  position,  restoring  the  original 
conditions  as  nearly  as  possible.  Be  sure  that  the  stops  do  not  prevent 
the  governor  from  shutting  off  but  do  prevent  it  from  straining  any  of 
the  mechanism.  Be  sure  that  the  friction  of  the  drag  spring  or  other 
parts  has  not  been  made  excessive  by  the  change.  The  wheel  must  then 
be  re-balanced  as  explained  in  the  note  of  the  following  section. 

251.  The  Balance  Of  A  Shaft  Governor  And  Its  Flywheel 

are  important  features  of  design.  If  the  moving  parts  of  a 
governor  have  no  tendency  to  rotate  about  their  pivots,  due 
to  gravity,  when  the  governor  is  at  rest,  the  governor  itself 
is  said  to  be  in  balance.  If  a  governor  is  not  in  balance,  it 
will,  when  the  engine  is  running  slowly,  tend  to  deflect  first 
one  way  and  then  another.  A  governor  flywheel  is  in  balance 
if  its  center  of  gravity  lies  in  the  axis  about  which  it  revolves. 
If  the  flywheel  is  not  balanced  it  will,  when  the  engine  is 
running,  produce  a  centrifugal  force  acting  at  its  center  of 
gravity.  This  centrifugal  force  will  produce  undue  pressures 
in  the  main  bearings  and  excessive  bending  stresses  in  the 
crank  shaft.  The  balance  of  a  governor  flywheel  may  or  may 
not,  depending  on  its  construction,  be  destroyed  as  the 
weights  assume  different  positions  at  various  engine  speeds. 
A  governor  flywheel  is  in  continual  balance  when,  as  the  weights 


236     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  7 


I- Enlarged   tnd 
View  Of  Shaft 


^Orease  Spot 

\5haft  Center 

-Scribed Circle  Off  Center 


deflect  with  centrifugal  force,  its  balance  is  not  destroyed. 
If  a  governor  flywheel  is  not  in  continual  balance,  it  will, 
theoretically,  be  out  of  balance  at  some  governor  position. 
But  the  flywheel  may  be  balanced  for  a  certain  position  of  its 
weights  by  bolting  weights,  W  (Fig.  299),  at  the  proper  points 
to  the  flywheel  rim.  It  is  possible  for  a  governor  itself  to  be 

in  balance  without  the  flywheel 
being  balanced  for  any  or  all 
positions  of  the  weights.  Ex- 
amples of  various  degrees  of  gov- 
ernor and  flywheel  balance  are 
given  in  the  following  section. 

NOTE. — IF  THE  FLYWHEEL  HAS 
BECOME  UNBALANCED  due  to  revers- 
ing the  engine  or  other  alterations, 
the  balance  may  be  restored  as  follows : 
First  find  the  direction  of  the  un- 
balanced force.  To  do  this,  smear 
grease  or  chalk  or  some  other  material 
on  the  end  of  the  shaft  near  the 
center,  as  shown  in  /,  Fig.  299,  so 
that  a  scribed  line  will  show  on  it. 
Arrange  a  block,  box  or  chair  so  as 
to  support  or  steady  a  scriber  near 
the  shaft  center  and,  while  the  engine 
is  running,  scribe  a  small  circle  on 
the  end  of  the  shaft.  If  the  center  of  the  scribed  circle  is  not  in  the 
center  of  the  shaft,  the  flywheel  is  out  of  balance.  Weight  must  then  be 
added  to  the  flywheel  rim  at  a  point  located  by  drawing  a  line  from 
the  shaft  center  through  the  center  of  the  scribed  circle  and  extending 
this  line  to  the  rim.  The  amount  of  the  balancing  weight  which  is 
required  may  be  found  by  first  sticking  a  lump  of  putty  or  clay  to  the 
rim  and  making  another  scribed  circle.  When  the  right  amount  of  clay 
to  insure  balance  is  found  in  this  way,  select  a  piece  of  metal  of  the  same 
weight  as  the  clay.  Bolt  the  metal  to  the  flywheel  rim  with  a  counter- 
sunk machine  bolt. 

252.  Shaft  Governors  May  Be  Classified  With  Respect 
To  The  Arrangement  of  Weights  Employed  as  follows: 
(1)  Balanced  governors  with  two  weights  and  their  flywheels  in 
continual  balance,  as  shown  in  Figs.  300  and  301.  (2)  Balanced 
Governors  with  a  single  weight  and  their  flywheels  not  in  continual 
balance  (Fig.  302) .  (3)  Governors  with  a  single  arm  which  carries 


H-Weights  For  Restoring 
Balance  To  Flywheel 

Fia.  299. — Illustrating  a  method  of 
balancing  a  flywheel.  (Governor 
wheel  of  a  Troy  automatic  engine.) 


SEC.  252]        SHAFT  STEAM-ENGINE  GOVERNORS 


237 


Direct  ion  Of 
Rotation  --, 


inertia  weight,  centrifugal  weight  and  eccentric  (Fig.  303); 
the  governor  and  its  wheel  being  nearly  balanced  in  all  posi- 
tions. The  action  of  governors  of  this  type  was  explained  in 
Sec.  247.  (4)  Governors 
having  two  arms  or  an  arm 
and  a  weight,  the  governor 
and  its  wheel  being  nearly 
balanced  in  all  positions 
(Figs.  291  and  304).  Gov- 
ernors of  all  of  the  above 
classes  can  be  so  operated 
that  the  regulation  is  either 
assisted  or  retarded  by  in- 
ertia and  can  be  connected 
to  a  rotating  or  a  swinging 
eccentric  as  desired.  In 

mOSt  Of  the  governors  here         FIQ.    SOO.— Shaft   governor   which   employs 
described,  the  inertia  aSSistS    two    weights.     (Governor    balanced   and    fly- 
.  wheel  in  continual  balance.) 

the  regulation.     See  Table 

254  for  manufacturers  of  engines  which  employ  governors  of 

the  various  kinds. 


Spring 
"Tension 
Adjustment 


Weight 


Direction  of 
Rotation^ 

Leaf 


EXAMPLES. — Figs.  300  and  301  show  governors  of  Class  1  having  two 
weights,  W,  in  balance.  The  eccentric  (Fig.  300)  is  mounted  on  a  plate, 
G,  pivoted  at  P  and  is  connected  to  weight  levers, 
WE,  by  connecting  rods  in  such  a  manner  that 
the  action  of  centrifugal  force,  in  throwing  the 
weights  WW  outward,  causes  the  center,  R,  of  the 
eccentric  to  swing  toward  the  center,  0,  of  the 
shaft.  The  springs  pivoted  at  K  act  against 
the  centrifugal  force  and  hold  the  weights  in  a 
certain  position  for  each  speed.  The  dash-pot 
simply  restrains  the  motion  when  too  rapid  and 
tends  to  prevent  racing  and  hunting. 

Fig.  302  is  an  illustration  of  a  shaft  governor  the 
flywheel  of  which  is  not  in  continual  balance  (Class 
2) .  Although  this  governor  has  but  a  single  weight, 
B,  its  parts  are  nevertheless  balanced.  Its  ad- 
vantages over  governors  of  Class  1  are — a  lesser 
number  of  working  parts,  simpler  construction  and  less  friction.  An 
example  of  a  governor  of  this  class  the  Robb- Armstrong-Sweet  gover- 
nor (Fig.  309)  (see  Table  254). 


Flywheel'' 


FIG.  301.—  "Hard- 
wick"  shaft  governor  as 
used  on  the  Erie  engine. 


238     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  7 

Fig.  303  shows  a  governor  of  Class  3  which  has  a  nearly  balanced  single 
arm.  This  governor  is  of  the  Rites  type,  which  is  extensively  used  in 
the  United  States,  and  is  designed  to  take  full  advantage  of  inertia. 


•^Direct/on  Of 
tat/on 


FIG.  302. — Shaft  governor  employing  a  single  weight,  B,  balanced  by  the  eccentric,  P. 
(The  flywheel  balance  depends  on  the  position  of  B.) 


D/rec-f/'onOf..-- 
Rotation  - ' 


Stop-' 


•Drag 
Spring 


FIG.  303. — Rites  governor.  (This  governor  is  not  in  balance  nor  is  its  wheel  but  the 
flywheel  may  be  balanced  with  extra  weights  on  the  rim;  and  the  governor  may,  by 
friction,  be  prevented  from  knocking  at  low  speeds  so  that  satisfactory  results  may  never- 
theless be  obtained.) 


Fig.  291  is  an  example  of  a  governor  of  Class  4.  The  advantage 
claimed  for  it  by  the  manufacturers  is  close  regulation  without  the  use  of 
a  dash-pot  to  prevent  hunting. 


SEC.  253]         SHAFT  STEAM-ENGINE  GOVERNORS 


239 


NOTE. — Some  parts  of  the  following  text  is  based  on  material  from 
SHAFT  GOVERNORS  by  Hubert  E.  Collins;  other  parts  are  based  on  data 
from  instruction  books  of  the  various  engine  manufacturers. 

253.  The  Two  Methods  Whereby  The  Engine  Valves  May 
Be  Controlled  By  A  Shaft  Governor  Through  The  Eccentric 
Or  The  Valve-Operating  Crank  Phi,  either  of  which  may  be 
employed  in  any  given  governor,  are  as  follows:  (1)  The 
eccentric  is  rotated  or  twisted  around  the  shaft.  Thereby  the 


Centrifugal 

Adjustable      We/gthf^         Aafj'usfab/e 
Spring 
Tens/on^ 


/nerfia   Weights  •'' 


FIG.  304. — Chuse  Engine  Mfg.  Co.,  governor.  (This  governor  is  used  on  non-releasing 
Corliss-valve  engines  to  control  the  position  of  the  eccentric  which  operates  the  admission 
valves  only.  The  exhaust- valve-operating  eccentric  remains  fixed  in  position.) 


angular  advance  is  changed  without  change  of  eccentricity 
or  throw.  (2)  The  eccentric  is  mounted  on  a  disc  or  plate 
which  is  swung  by  the  governor  action  across  the  center  of  the 
shaft.  Thereby  the  throw  and  angular  advance  of  the  eccen- 
tric are  both  changed,  the  object  in  the  design  being  to  have 
the  lead  of  the  valve  change  but  slightly  with  different  governor 
positions.  With  either  of  the  above  classes  of  valve  gear,  the 
governor  may  employ  any  of  the  weight  arrangements  specified 
in  Sec.  252.  It  follows  that  the  weight  arrangement  of  a 
governor  does  not  determine  its  method  of  valve  control. 

NOTE. — A  SHAFT  GOVERNOR  OF  ANY  TYPE  MAY  USE  A  CRANK  PIN  IN 
PLACE  OF  AN  ECCENTRIC.  When  the  governor  is  at  the  end  of  the  shaft, 
a  crank  pin  is  usually  used.  When  the  shaft  continues  on  through  the 


240    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  7 

governor,  an  eccentric,  which  is  properly  slotted  to  permit  movement 
to  or  from  the  shaft  center  is  ordinarily  employed. 

EXPLANATION. — The  Buckeye  governor  of  Fig.  316  is  an  example  of 
Class  1.  The  eccentric,  C,  has  two  ears  which  are  connected  by  links 
to  the  ends  of  the  levers,  M.  As  the  weights,  A,  are  thrown  out  by 
centrifugal  force,  the  eccentric  is  rotated  in  the  direction  indicated.  Its 
angular  advance  is  thus  increased.  The  Fitchburg  governor  of  Fig.  320 
is  an  example  of  Class  2;  the  eccentric,  A,  is  so  arranged  that  its  throw 
and  angular  advance  are  both  varied,  see  Sees.  148  and  151,  giving  a 
practically  constant  valve  lead. 

254.  Table   Showing   Classification   Of   Shaft   Governors. 


Manufacturer 

Governor  name 

Fig. 
No. 

Class  by 
weight 
arrange- 
ment, 
Sec.  252 

Class  by 
eccentric 
arrange- 
ment, 
Sec.  253 

Ames  Iron  Works 

Robb-  Armstrong- 

Brownell  Co  

Sweet 
Rites 

310 
306 

2 
3 

2 
2 

Buckeye  Engine  Co  
Chandler  &  Taylor  
Chuse  Engine  Mfg.  Co.  . 
Erie   Ball   Engine   Co., 
Ball  engine. 
Erie  Engine  Works,  Erie 
engine             

Buckeye 
Armstrong 
Chuse 
Robb-Armstrong- 
Sweet 

Hard  wick 

316 
311 
304 

301 

1 
2 

4 

2 
1 

1 
2 
2 

2 
2 

Fitchburg 

Fitchburg 

320 

1 

2 

Harrisburg  i  

Fleming 

314 

1 

2 

Hooven-Owens-Rentch- 
ler  Co.,  Hamilton  en- 
gine 

Special* 

321 

1 

1 

A.  L.  Ide  &  Sons,  Ideal 
engine 
Liddell  Co 

|  Rites 
1  Armstrong 
Rites 

312 

306 

3 
2 
3 

2 
2 
2 

Nordberg    

Special* 

3 

2 

Ridgway                 

Rites 

308 

3 

2 

Skinner 

Skinner 

291 

4 

2 

Trov 

Rites 

307 

3 

2 

*  These  two  governors  are  not  shaft  governors  according  to  the  defini- 
tion in  Sec.  242,  but  are  in  a  class  by  themselves.  They  are  very  similar 
to  shaft  governors,  however,  and  because  of  their  importance  are  here 
included. 


SEC.  255]        SHAFT  STEAM-ENGINE  GOVERNORS  241 

256.  Some  Effects  Of  Weight  Or  Spring  Adjustment  On 
Shaft-Governor  Operation  may  be  stated  as  follows:  The 
sensitiveness  of  shaft  governors  and  the  speed  at  which  they  will 
regulate  depend  principally  on  the  following  conditions: 
(1)  Tension  of  springs.  (2)  The  distance  from  the  point  where 
the  springs  are  attached  to  the  weight  or  lever  pivot.  (3)  The 
sensitiveness  of  the  springs — that  is,  the  distance  they  will 
deflect  for  a  given  increase  in  force.  (4)  The  angle  at  which  the 
spring  acts  to  the  direction  which  the  governor  arm  or  weight 
tends  to  move.  (5)  The  mass  of  the  weight  which  produces 
centrifugal  force.  (6)  The  distance  of  the  center  of  gravity  of  the 
weight  from  the  fulcrum.  (7)  The  angle  between  the  direction  in 
which  the  weight  tends  to  move  and  that  in  which  it  is  free  to 
move.  Substituting  a  heavier  spring,  increasing  the  spring 
leverage,  or  shifting  the  spring  more  in  line  with  the  direction 
in  which  the  movable  end  of  the  spring  moves,  makes  the 
governor  less  sensitive.  Increasing  the  centrifugal  weight 
and  at  the  same  time  adjusting  the  spring  so  as  to  give  the 
same  speed  makes  the  governor  more  sensitive — in  fact,  the 
governor  may  thus  be  made  unstable.  Small  changes  in  speed 
may  be  made  by  changing  the  centrifugal  weight  or  spring 
tension  (whichever  is  recommended  by  the  manufacturer) 
without  any  other  apparent  effects. 


242    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  7 


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SEC.  257]         SHAFT  STEAM-ENGINE  GOVERNORS  243 

257.  Some  Troubles  Which  May  Be  Encountered  In 
Operating  Any  Shaft  Governor  and  their  remedies  are  as 
follows:  (1)  The  governor  is  sluggish.  Sluggishness  in  shaft 
governors  usually  results  from  one  of  two  causes.  Either 
there  is  too  much  friction  or  the  governor  is  too  nearly  neutral 
(isochronous)  to  be  stable.  The  friction  may  be  in  the  dash- 
pot  or  anywhere  in  the  mechanism  as  explained  in  the  following 
section.  If  the  dash-pot  resists  the  movement  of  the  governor 
too  much,  a  larger  hole  in  the  piston  or  larger  valve  opening 
or  a  lighter  oil  will  remedy  the  trouble.  If  the  governor  has 
been  adjusted  for  very  close  regulation,  it  may  lack  the  power 
to  change  its  position  promptly.  The  remedy  (Table  256) 
is  to  increase  the  weight  and  use  a  stronger  spring  so  that  the 
original  speed  is  obtained  or  to  increase  the  spring  leverage 
where  means  of  so  doing  is  provided.  Governors  of  the 
Robb-Armstrong-Sweet  type  (Sec.  263)  may  be  sluggish  when 
adjusted  for  too  much  regulation. 

(2)  The  governor  hunts.     This  may  be  due  to  very  close 
regulation  with  a  free-moving  governor.     It  may  usually, 
under  these   conditions,   be   corrected  by  introducing  more 
friction  by  means  of  a  drag  spring  or  preferably  a  dash-pot. 
If  good  action  cannot  be  secured  in  this  way,  the  governor 
should     be     adjusted     for     larger    regulation    as    explained 
above.- 

(3)  The  engine  speeds  up  or  races.     The  spring  may  be 
entirely  too  tight  or  too  stiff  for  the  desired  speed.     The 
weights  may  be  much  too  light  or,  in  the  Rites  type  (Sec.  260), 
too  nearly  balanced  about  the  weight  pivot.     Under  these 
conditions,  adjust  the  weight  and  spring  for  the  desired  speed. 


NOTE. — RACING  Is  MOST  FREQUENTLY  CAUSED  BY  FRICTION  of  parts 
or  other  local  troubles.  There  is,  however,  a  noticeable  difference 
between  racing  caused  by  over-sensitiveness  or  too  weak  springs  and  that 
caused  by  friction.  When  it  is  caused  by  spring  tension  alone,  the 
changes  in  speed  will  be  rapid,  even,  and  within  a  certain  range.  When 
caused  by  friction,  the  weights  will  stick  in  their  inner  position  until 
the  speed  developed  is  so  high  as  to  throw  them  out;  or,  when  the  engine 
is  above  speed,  they  will  stick  where  they  are  until  the  speed  is  reduced 
enough  for  the  springs  to  draw  them  back  again.  Such  changes  are 
usually  accompanied  by  noise  when  the  change  takes  place. 


244    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  7 

258.  Most  Troubles  With  Shaft  Governors  Are  Due  To 
Some  Part  Of  The  Mechanism  Sticking  or  not  moving 
freely.  All  of  the  well-known  makes  of  modern  shaft 
governors,  regardless  of  their  class,  are  thoroughly  adjusted, 
tested,  regulated,  and  set  by  their  makers  usually  before  they 
are  shipped  from  the  factory.  Hence,  when  they  are  delivered 
to  the  operating  engineer,  they  should  regulate  within  the 
guaranteed  speed  range.  The  difficulties  which  arise  after 
the  governors  have  been  in  service  for  an  extended  period 
usually  are  due  to  wear  or  to  an  accidental  cause,  and  usually 
can  be  remedied  readily.  After  a  governor  has  been  perfected 
and  has  run  satisfactorily,  there  is  no  reason  why  it  cannot 
be  restored  to  its  original  condition.  Often  the  trouble  is  a 
slight  one,  so  small  as  to  be  overlooked. 


Connecting 
Strap 


Valve  •' 


FIG.  305. — Sweet  governor,  operating  gridiron  valve. 


EXAMPLES. — An  engineer  may,  with  a  spanner  wrench,  give  the  valve- 
rod  gland  a  half  turn  to  tighten  it  up;  this  may  cause  the  engine  to 
run  away.  An  engine  having  a  Sweet  governor  (Fig.  305)  may  race  if  a 
single  very  small  grain  of  gravel,  G,  gets  between  the  band  which  connects 
the  spring  and  the  weight  arm  and  the  weight  arm  itself.  Again,  a  cap 
which  pinches  on  one  of  the  fulcrum-pins  or  a  slight  burr  on  a  valve-rod 
has  caused  trouble  in  a  governor.  The  slightest  thing  should  not  be 
overlooked.  Dry  pins  often  cause  trouble.  Hence  a  governor  should 
be  oiled  as  regularly  as  any  other  part  of  the  engine.  About  once  a 
month,  when  the  engine  is  operating  continually  in  a  dirty  atmosphere, 
all  pins  and  bearings  should  be  taken  apart  and  cleaned. 

When  a  search  for  trouble  begins,  nothing  should  be  neglected  from 
the  governor  eccentric  to  the  farthest  edge  of  the  valve  in  the  valve 


SEC.  259]        SHAFT  STEAM-ENGINE  GOVERNORS  245 

chest.  Disconnect  the  eccentric  rods  from  the  governor  eccentric 
and  remove  or  release  the  spring  or  springs  from  the  weight  arm  or 
arms.  Then  move  the  weight  arms  in  and  out  from  inner  to  outer 
positions.  Most  of  the  shaft  governors  on  engines  from  5  h.p.  to  1,000 
h.p.  are  so  counterbalanced  that,  when  thus  dismantled,  one  man 
should  with  the  smaller  engines  be  able  to  easily  move  the  parts  in  and 
out  with  one  hand.  On  the  larger  engines,  he  should  be  able  to  do  this 
with  both  hands  but  he  should  never  use  a  bar  of  any  kind. 

If  the  weight  arms  do  not  move  with  sufficient  freedom  to  permit  this, 
the  trouble  is  probably  caused  by  dry  or  cut  pins,  pinching  caps,  bent 
rods  or  links  which  make  the  pins  bind,  pinching  or  dry  eccentric  straps, 
or  the  eccentric  binding  (in  some  instances  between  a  bearing  and 
governor-wheel  hub).  Or  sometimes  gummed  oil  and  grit  cause  it. 

If  the  governor  is  free  and  in  perfect  condition,  disconnect  the  valves 
from  the  rockers  or  valve-rod  slides,  as  the  case  may  be.  Then  look  for 
dry  surface  of  pins  or  bearings  or  slides,  bent  rods  and  other  like  condi- 
tions. This  done,  see  that  the  valve  stems  are  straight  and  true,  and  in 
line  with  their  connections;  also  that  their  bearings  do  not  bind  and  are  not 
dry.  See  whether  they  are  burred  or  are  worn  so  small  in  the  stuffing 
box  that  the  packing  when  pulled  tight  binds  the  stems.  Note  whether 
the  packing  is  old  and  dry. 

Look  into  the  steam  chest.  See  if  the  valve  is  set  properly  and  if  it 
leaks  or  if  the  pressure-plate  binds.  Often  an  engineer  forgets  that 
proper  valve  setting  (see  Div.  4)  is  as  essential  as  it  is  to  have  the  governor 
free  and  well  lubricated. 

NOTE. — GREASES  AND  LUBRICANTS  WHICH  DRY  OUT  AND  LEAVE 
DEPOSITS  SHOULD  BE  CAREFULLY  AVOIDED  FOR  SHAFT  GOVERNORS. 
A  thin  grease,  the  consistency  of  vaseline,  is  preferable  for  the  roller 
bearings  and  pins.  Cylinder  oil  is  satisfactory  for  the  smaller  pivots. 
The  roller  bearings  should  preferably  be  examined,  cleaned  and  oiled 
monthly. 

259.  In  Adjusting  Shaft  Governors,  the  engineer  should  first 
make  sure  that  the  main  pin  or  pins  and  their  bushings  are  free 
and  properly  lubricated,  and  that  the  valve  is  properly  set  and 
runs  freely.  If  the  arm  is  heavy  enough  to  drive  the  valve,  see 
whether  the  desired  governing  effect  can  be  produced  by 
adjusting  the  spring.  Avoid  adding  unnecessary  weights 
and  the  consequent  overstraining  of  springs,  bushings  and 
pins. 

NOTE. — IT  MAY  BE  NECESSARY  To  ADJUST  THE  SHAFT  GOVERNOR 
WITH  No  OTHER  DATA  THAN  THAT  WHICH  BECOMES  AVAILABLE  FROM 
WATCHING  THE  ELECTRICAL  SWITCHBOARD  METERS,  while  the  engine  is 
running  in  service.  The  proper  remedy  for  the  apparent  fault  may  be 


246     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE      [Div.   7 

applied  on  the  occasion  of  the  next  shut-down.  It  may  take  an  hour's 
careful  watching  of  the  switchboard  instruments  to  determine  the  real 
action  of  the  governor.  The  only  certain  procedure  is  to  wait  for  the  load 
to  so  change  that  the  symptom  for  which  one  is  watching  will  be  shown. 
That  is,  the  load  should  remain  constant  long  enough  to  give  the  engine 
time  to  attain  a  constant  speed.  The  observations  should  be  repeated 
until  the  exact  constant  speeds  under  several  different  loads  are 
ascertained. 

NOTE. — A  COMMON  CAUSE  OF  COMPLAINT  WITH  SHAFT  GOVERNORS 
Is  HAMMERING  of  the  weighted  arm  on  the  stops  in  starting  or  shutting 
down  the  engine.  This  can  often  be  overcome  on  a  Rites  type  governor 
by  moving  the  attached  weights  and  noting  whether  hammering  is 
increased  of  diminished.  Usually  the  proper  change  is  to  add  weight  on 
the  spring  side  of  the  arm  and  to  increase  the  spring  tension,  though  it 
may  be  necessary  to  add  weight  at  both  ends.  It  is  a  peculiar  fact  that 
friction  in  the  valve  gear  operates  to  help  the  governor  spring  so  that 
an  engine  may  be  speeded  up  several  revolutions  by  excessively  tight 
valve-stem  packing  or  any  similarly  acting  cause.  It  is  well  to  look 
over  the  valve  motion  as  a  possible  cause  of  any  unaccountable  change 
of  speed.  If  a  brake  or  drag  spring  is  used  on  the  governor  the  friction 
may  be  increased  to  prevent  hammering;  but  if  it  is  set  up  too  tightly,  it 
may  cause  continual  changes  of  speed  through  its  action  in  checking  the 
governor  arm  as  it  swings  out  or  in,  and  so  prevent  the  arm  from  floating 
gradually  to  the  proper  position. 

260.  The  Rites  Governor  Is  Used  By  A  Number  Of  Different 
Engine  Manufacturers:  see  Table  254.     The  action  of  this 
governor  was  explained  in  Sec.  247.     In  practice,  as  the  load 
increases,  this  governor  usually  changes  not  only  the  throw  of 
the  eccentric  but  also  its  angular  advance.     Thus,  the  points 
of  compression  and  cut-off  are  advanced  but  the  lead  remains 
practically    constant.     The    movement   of   the    governor    is 
much  exaggerated  in  Figs.  295  to  298.     The  actual  layout  is 
shown  in  Fig.  306.     The  Rites  governor  as  used  on  the  Troy 
vertical  engine  is  shown  in  Fig.  307,  and  on  the  Ridgway  engine 
in  Fig.  308. 

261.  Rites  Governors  Are  Sometimes  Provided  With  Dash- 
Pots  Or  Drag  Springs  For  Limiting  The  Rate  Of  Movement. 
The  dash-pot,  G  (Fig.  308),  is  filled  with  oil  for  side-crank 
engines  and  with  air  for  center-crank  engines.     A  plug  having 
an  opening  of  proper  size  is  inserted  in  the  bottom  of  the 
air-filled  pot  to  regulate  the  rate  of  movement.     A  by-pass 
and   valve  are  provided  for  regulating  some  oil  dash-pots. 


SEC.  261]         SHAFT  STEAM-ENGINE  GOVERNORS 


247 


Others  are   controlled  by  holes  in  the   pistons   (Sec.   230). 
Air  dash-pots  are  more  likely  to  give  trouble  from  sticking  with 


Inert/a 

Direction        (Weight^ 
Of  Rotation 


Direction  Of 
Rotation 


Center  Of  Gravity 
Weight  A 


Governor 

***--., 

Vafve-Rod 
Pin- 
Center  Of 
Gravity 
Weight 
B 


"Imaginary 
Line  Joining  Centers 
Of  Gravity 

FIG.  306. — Lay-out  of  Rites  gover- 
nor. (The  locations  of  the  centers  of 
gravity  in  A  and  B  may  be  shifted  by 
adding  movable  weights  to  or  remov- 
ing movable  weights  from  them,  or  by 
shifting  the  position  of  the  movable 
weights.) 


Running _.. 
Over  - ' ' 


FIG.    307. — Governor    of   the    Troy    vertical 
engine.     (Rites  type.) 


Adjustable 
'  Weight 


FIG.  308. — Governor  of  the  ridgway  automatic  engine.     (Rites  type.) 


dirt  than  are  oil  dash-pots  and  should  therefore  be  closely 
watched  and  lubricated  with  cylinder  oil.  Dash-pots  may  be 
adjusted  for  greater  or  less  promptness  as  explained  in  Sec. 


248    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  7 

233,  Div.  6.  The  drag  spring,  S  (Fig.  307)  ,  introduces  mechan- 
ical friction  to  prevent  too  much  movement  of  the  governor. 
There  is  ordinarily  sufficient  vibration  of  the  engine  to  prevent 
such  springs  from  making  the  governor  bind  when  in  the 
wrong  position. 

262.  Some  Special  Adjustments  Of  The  Rites  Governor 
(Fig.  306)  are  as  follows:  (1)  Shifting  the  movable  weights, 
which  are  frequently  provided,  from  W  to  X  or  from  Y  to  Z 
increases   the   weight   leverage;  see  Table  256.     (2)  Shifting 
movable  weights  from  B  to  A  increases  the  centrifugal  weight. 
Removing  weights  from  positions  B,  W  or  Y  has  an  effect 
similar  to  that  of  adding  them  at  Z,  A  or  X.     Shifting  the 
spring  pivot,  S,  farther  from  the  governor  pivot,  G,  decreases 
the  sensitiveness. 

263.  The    Robb  -Armstrong-Sweet    Governor,     which    is 
used  by  many  manufacturers  (see  Table  254),  is  shown  in 


.•Direction  Of 


FIG.  309. — Simple  Robb-Armstrong-Sweet  governor. 

Figs.  309  to  313.  This  governor  is  placed  in  the  second  class 
in  Sees.  252  and  253.  The  weight,  W,  is  fastened  directly  to 
the  spring,  S,  which  is  secured  to  the  flywheel  rim,  F,  or  spoke. 
The  tension  on  the  spring  is  changed  by  taking  up  or  slackening 
the  tension-studs,  B.  The  eccentric  arm,  A,  is  pivoted  at  P, 
moving  the  eccentric  or  eccentric  pin,  R,  which  changes  the 
travel  of  the  valve  and  the  point  of  cut-off.  The  arm,  A, 
is  actuated  by  the  spring  by  means  of  one  link,  L,  one  end  of 
which  can  be  changed  in  its  position  by  shifting  the  pin  into 
any  one  of  the  series  of  holes  shown. 


SEC.  264]         SHAFT  STEAM-ENGINE  GOVERNORS 


249 


NOTE. — IN  ADJUSTING  ROBB-ARMSTRONG-SWEET  GOVERNORS:  To 
increase  the  speed,  give  more  tension  on  the  spring.  To  decrease  the  speed, 
give  less  tension  on  the  spring.  To  get  closer  regulation  and  sensitiveness, 
move  the  pin,  E,  in  the  eccentric  lever  closer  to  the  shaft  center.  To 


Slot  For 
Adjusting  For 
Different 
Sensitiveness 


Spring  Tension  Adjustment 
For  Different  Speeds 


'ccentric 
Rod 


FIG.  310. — Governor  of  the  Ames  engines. 
(Robb-Armstrong-Sweet  type.) 


Fia.    311. — Governor    of    Chandler    & 
Taylor  engine.     (Armstrong  type.) 


make  more  stable  and  sluggish,  and  prevent  racing,  move  the  pin,  E,  closer 
to  the  rim  of  the  wheel.  No  change  of  weight  is  provided  for,  as  the 
above-suggested  adjustments  are  considered  by  the  makers  to  be  sufficient 
to  cover  all  requirements. 


Weight 


f/y  wheel- 


Pivot  Pi 


Adjusting 
Bolt       -•• 


'heel 


FIG.  312. — Side  view  of  shaft  governor  of  the 
"Ideal"  Corliss-valve   engine. 


Counter- 
balance 
Weight 

Bosses  For 

Governor 

Attachment 

FIG.  313. — Sectional  elevation 
of  "Ideal"  Corliss- valve  engine 
shaft  with  governor  mechanism 
removed. 


264.  The  Principal  Adjustments  Of  The  Fleming-Harris- 
burg  Engine  Governor  (Fig.  314)  in  their  recommended  order 
are:  (1)  For  greater  or  less  speed,  increase  or  decrease  the 
weights,  W,  in  the  centrifugal  (larger)  weight  pockets,  keeping 


250    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  7 

them  equal  in  the  two  larger  weight  pockets.  (2)  If  more 
speed  adjustment  is  required,  vary  the  spring  tension.  (3) 
For  more  sensitiveness,  shift  the  traversing  blocks,  B,  in  the 


Traverse  Block 


Fid.  314. — Fleming-Harrisburg  centrally  balanced  centrifugal  inertia  governor.     This 
shows  a  right-hand  governor,  engine  running  over. 

slots  farther  from  the  centrifugal  weights.  For  less  sensitive- 
ness— more  stability — shift  the  blocks  closer  to  the  centrifugal 
weights. 

Direction  Of 
Rotation 


FIG.  315. — American-Ball  engine  governor. 

265.  The  American-Ball  Engine  Governor  (Fig.  315)  is  of 
class  4,  Sec.  252.  The  advantage  of  the  two  springs,  D  and  C, 
is  that  there  is  little  bowing  outward  of  the  springs  with  cen- 


SEC.  266]         SHAFT  STEAM-ENGINE  GOVERNORS 


251 


trifugal  force  with  this  spring  arrangement.  If  spring  C 
is  slackened,  and  spring  D  tightened,  the  governor  will  be 
more  sensitive.  If  both  are  tightened  at  once  by  nut  F, 
the  speed  will  be  increased. 

266.  The  Buckeye  Governor  (Fig.  316))  has  several  unique 
features.  It  controls  only  the  cut-off  eccentric.  The  Buckeye 
engine  is  fitted  with  a  fixed  eccentric  which  controls  the  other 


Tension 


FIG.    316. — Buckeye    engine   governor.     (Employs   two    weights    in  gravity  balance 
changes  only  angle  of  advance.) 

steam  events — namely,  release,  compression  and  admission. 
The  governor  changes  only  the  point  of  cut-off.  This  governor 
changes  only  the  angular  advance  of  the  eccentric.  The  travel 
of  the  valve  therefore  remains  constant.  An  advantage  claimed 
for  this  method  of  governing  is  that  the  valve  which  has  a 
constant  travel  wears  the  valve  seat  evenly.  If  the  valve 
travel  is  less  under  light  than  under  heavy  loads,  shoulders 
may  be  worn  on  the  seat  at  the  ends  of  the  valve  travel  when 
the  engine  is  running  under  light  load.  The  valve  will  then 
strike  these  shoulders  when  an  extra  load  is  put  on  the  engine. 


252    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  7 


EXPLANATION. — The  weights,  A  (Fig.  316),  are  mounted  on  weight 
arms,  M,  which  are  pivoted  at  N.  The  links,  B,  connect  the  weight- 
arm  ends  to  the  ears  of  the  eccentric,  C.  When  the  weights,  A,  are 
moved  outward  by  centrifugal  force  against  the  tension  of  springs,  F, 
the  eccentric  may  be  turned  a  maximum  of  90  deg.  around  the  shaft 
as  a  center.  Springs,  F ' ,  are  fastened  to  arms,  M,  by  means  of  spring 
clips,  D,  which  may  be  adjusted  on  the  arms  to  increase  the  leverage 
of  the  spring  and  thereby  increase  its  effective  strength.  The  outer 
ends  of  the  springs  are  connected  to  the  rim  of  the  flywheel  by  tension 
screws,  S,  by  which  the  tension  of  the  springs  may  be  varied.  The 
auxiliary  leaf  springs,  P,  act  against  the  spring  studs,  T,  and  have 
the  effect  of  increasing  the  spring  tension  near  the  minimum-speed 
position.  The  rollers,  G,  prevent  the  springs  from  bowing  outward 
due  to  centrifugal  force,  at  speeds  of  250  r.p.m.  or  more. 

NOTE. — SOME  SPECIAL  TROUBLES  OF  THE  BUCKEYE  GOVERNOR  AND 
THEIR  REMEDIES  are;  see  Fig.  316.  Auxiliary  springs,  P,  too  weak.  The 
performance  when  these  springs  are  too  weak  will  be  the  same  in  kind 

as  though  they  were  absent  entirely, 
though  more  moderate  in  degree. 
On  starting,  the  engine  will  run  above 
its  proper  speed  before  the  levers,  M, 
will  expand.  Then  they  will  fly  out 
violently.  Stable  regulation  will  be 
possible  only  with  loads  so  light  as 
to  regulate  at  one-fourth  stroke  cut- 
off or  earlier.  That  is,  stable  regula- 
tion can  be  obtained  only  with  loads 
such  as  require  the  levers  to  act  solely 
in  the  outer  half  of  their  range  of 
movement.  At  heavier  loads,  the 
governor  will  race  continually.  The  effective  strength  of  the  auxiliaries 
may  be  increased  by  lengthening  the  spring  stud  as  from  V  to  X  (Fig.  317). 
Auxiliary  springs,  P,  too  strong.  On  starting  up,  the  levers  will  move 
out  at  noticeably  less  than  rated  speed  and  expand  gradually  as  the  speed 
increases  till  the  limit  of  the  follow  of  the  auxiliary  springs  is  reached. 
Then,  if  they  are  much  too  strong,  the  expanding  movement  will  tempo- 
rarily cease  until  normal  speed  is  reached,  when  they  will  finish  their 
expansion  with  proper  promptness.  The  regulation  will  be  the  same  as 
in  the  previous  case  when  the  load  was  too  light  to  bring  the  auxiliary 
springs  into  action.  But,  with  heavier  loads,  the  speed  will  be  slow  in 
proportion  to  the  undue  strength  of  the  springs.  At  maximum  load,  that 
is,  just  sufficient  load  to  bring  the  levers  to  their  inner  stops,  the  speed 
will  be  reduced  to  about  what  was  required  to  start  them  out.  In  all 
of  the  foregoing  cases,  the  tension  of  the  main  springs  was  assumed  to  be 
what  it  should  be  with  the  auxiliaries  at  their  best  adjustment.  That 
tension  of  the  main  springs  which  may  be  carried,  without  racing  at  any 
load,  is  always  less  than  will  be  required  when  auxiliary  springs  are  applied. 


FIG.  317. — Adjustable  spring  stud  for 
auxiliary  springs  of  Buckeye  governor. 


SEC.  267]        SHAFT  STEAM-ENGINE  GOVERNORS 


253 


267.  The  Mclntosh  &  Seymour  Engine  Governor  (Figs. 

318  and  319)  is  itself  balanced  and  its  flywheel  is  in  continual 
balance.     Like   the   Buckeye  governor,  it  controls  a  cut-off 


FIG.  318. — Mclntosh  &  Seymour  engine  governor  fully  deflected.     (No-load  position.) 

eccentric  only  by  varying  its  angle  of  advance.  The  weights, 
C,  are  deflected  outward  by  centrifugal  force  against  the 
tension  of  the  leaf  springs,  A.  The  governor  may  be  adjusted 


Direction  Of 


FIG.  319. — Mclntosh  &  Seymour  engine  governor  at  rest. 

for  greater  spring  tension  at  B  and  for  greater  centrifugal 
weight  by  adding  lead  weights  to  the  pockets,  C.  The  manu- 
facture of  this  engine  and  governor  has  been  discontinued. 


254     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  7 

268.  The  Fitchburg  Governor  (Fig.  320)  employs  two 
weights,  HH,  which  are  balanced  with  the  other  governor 
parts,  and  moves  the  eccentric  in  a  straight  line,  thereby 
varying  its  throw.  For  the  larger  engines,  the  governor  is 
mounted  within  a  wheel-like  casting,  called  a  governor  case, 
which  is  clamped  to  the  engine  shaft. 

NOTE. — IN  SETTING  THE  FITCHBURG  GOVERNOR,  the  location  of  the 
governor  case,  K  (or  flywheel  when  the  governor  is  mounted  within  a 
flywheel),  is  determined  by  placing  the  engine  on  one  dead  center  and 
rolling  the  case  around  the  shaft  until  the  offset,  0,  of  the  eccentric 

Direction  Of 
Rotation^ 


FIG.  320. — Fitchburg  governor.     (The  legend  "Crank  Pin"  means  that  the  crank  pin  is 
located  in  the  position  indicated  by  the  arrow.     The  crank  pin  is  not  shown.) 

is  on  the  opposite  side  of  the  shaft  from  the  crank-pin.  Then  roll  K 
carefully  into  such  a  position  that  when  (with  the  springs  removed) 
the  eccentric,  A,  is  thrown  back  and  forth  across  the  shaft,  no  end 
motion  is  given  to  the  valve  rod.  At  this  place  tighten  the  governor 
case  firmly  upon  the  shaft.  Turn  the  engine  to  the  opposite  dead 
center,  and  again  move  the  eccentric  back  and  forth  across  the  shaft. 
If  there  is  at  this  end  any  end  motion  to  the  valve  rod,  change  the 
position  of  the  governor  case  on  the  shaft  enough  to  make  the  motion 
just  half  as  much,  then  fasten  the  governor  case  firmly  in  this  final 
position  by  drilling  into  the  shaft  for  the  point  of  the  set  screw  and 
then  tightening  the  clamp-bolts  to  place  solidly.  Put  in  the  springs,  C, 
and  tighten  them  until  the  engine  operates  at  the  proper  speed.  Be  sure 
to  tighten  up  the  springs  that  go  through  the  counterbalance  which  hangs 
nearest  the  pin  B  (when  the  governor  is  at  rest)  about  three-fourths 
of  an  inch  more  than  the  springs  on  the  other  side. 


SEC.  269]         SHAFT  STEAM-ENGINE  GOVERNORS 


255 


NOTE. — WHEN  IT  Is  DESIRED  To  CHANGE  THE  DIRECTION  OF  ROTA- 
TION OF  A  FITCHBURG  ENGINE,  a  new  eccentric  must  be  procured  from 
the  makers  and  put  on  in  place  of  the  one  on  the  governor.  The  ends  of 
the  links  which  connect  the  weight  arms  must  be  changed  on  the  counter- 
balance weight- arm  end,  to  the  holes  opposite  to  those  which  they 
occupied  when  the  old  eccentric  was  used. 

269.  The  Governing  Mechanism  Of  The  Hamilton  Uniflow 
Engine  is  shown  in  Figs.  321  to  323.  Centrifugal  force  is 
developed  in  two  flat  curved  weights,  W  (Fig.  322),  which  are 


Wedge  For  Raising  Spring-Adjustment 


FIG.  321. — Longitudinal  section  of  governor  of  the   Hamilton  uniflow  poppet-valve 

engine. 


pivoted  at  P.  These  deflect  outward,  rotating  the  eccentric 
mounting,  E,  through  the  geared  sectors,  G.  The  rotation 
of  the  eccentric  is  opposed  by  the  spring  S,  through  the  arm, 
A  (Fig.  323).  The  tension  on  the  spring,  S,  may  be  adjusted 
when  the  governor  is  at  rest  by  the  screw,  N.  This  tension 
may  also  be  adjusted  when  the  engine  is  running  by  means  of 
the  handwheel,  L  (Fig.  321).  This  wheel  is  mounted  on  a 
screw-threaded  sleeve  which  forces  the  wedge,  R,  against  the 
screw,  N,  when  L  is  turned.  The  movement  of  N  is  com- 
municated to  spring  S,  through  the  spring-mounting  lever,  M. 


256    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE      [Div.  7 


By  thus  changing  the  spring  tension,  the  speed  at  which  the 
governor  controls  the  engine  may  be  changed. 


Direction  Of 
Rotation 


.Weight 


R     Direction  Of 
Dotation  -. 


FIG.  322. — Hamilton  uniflow-engine 
governor  showing  weights  and  eccen- 
tric-rotating sectors. 


FIG.  323.— Hamilton  uniflow-engine 
governor  showing  screw  for  spring- 
tension  speed  adjustment. 


270.  Setting  The  Valves  Of  An  Automatic  Engine  consists 
mainly  in  adjusting  the  length  of  the  valve  stem.  Shaft 
governors  are  nearly  always  keyed  to  the  shaft  and  so  the 
position  of  the  governor  is  fixed  and  determines  the  position 


Direction  Of 
Rotation 


FIG.  324. — Showing  governor  blocked  in  extreme  short-travel  position. 

of  the  eccentric.  If  it  is  desired  to  change  a  shaft  governor 
for  greater  or  less  equal  lead  (see  Sec.  174)  a  new  keyway  must 
be  cut.  The  valve  travel  of  an  automatic  engine  usually 
varies  with  the  load  and  is  determined  by  adjustment  of  the 
governor.  Directions  for  valve  setting  are  given  in  Div.  4. 


SEC.  270]         SHAFT  STEAM-ENGINE  GOVERNORS  257 

Fig.  324  illustrates  the  method  of  blocking  a  flywheel  governor 
when  the  valves  are  being  set. 

QUESTIONS  ON  DIVISION  7 

1.  What  is  a  shaft  governor?     An  automatic  engine? 

2.  How  does  the  governing  action  of  a  shaft  governor  and  slide  valve  differ  in  economy 
from  that  of  a  throttling  governor?     From  that  of  a  fly-ball-governed  Corliss  releasing 
gear? 

3.  Why  must  a  shaft  governor  exert  more  force  for  a  given  service  than  must  a  fly-ball 
governor? 

4.  Explain  by  a  sketch  the  action  of  a  shaft  governor  which  is  affected  by  centrifugal 
force  alone.     Why  must  some  speed  change  occur  in  order  that  a  centrifugal  governor 
may  operate? 

5.  What  is  the  principle  of  inertia?     How  is  it  employed  in  shaft  governors?     Why 
cannot  inertia  be  used  in  a  shaft  governor  as  the  only  governing  force? 

6.  Explain  how  inertia  and  centrifugal  force  come  into  play  in  inertia  governors. 
Why  is  it  more  necessary  to  employ  inertia  in  shaft  governors  than  in  fly-ball  governors? 

7.  What  difficulties  are  encountered  in  reversing  shaft-governed  engines?     Why  must 
the  flywheel  usually  be  rebalanced  after  a  governor  has  been  reversed? 

8.  When  is  a  shaft  governor  said  to  be  balanced?     Its  flywheel?     When  in  continual 
balance? 

9.  Explain  how  the  balance  of  a  flywheel  may  be  restored. 

10.  Name  four  classes  of  governor  weight  arrangement  and  name  a  manufacturer  of 
governors  of  each  class. 

11.  What  are  the  two  methods  of  valve  control  through  the  eccentric?     Name  a 
governor  which  uses  each  method. 

12.  Which  of  the  above  methods  of  valve  control  is  largely  used  with  simple  slide- 
valve  automatic  engines? 

13.  What  are  the  principal  methods  of  changing  the  speed  of  a  shaft-governed  engine? 

14.  How  may  the  sensitiveness  of  a  governor  be  decreased  when  there  is  no  means  of 
changing  the  spring  leverage? 

15.  What  is  one  cause  of  excessive  hunting  of  a  shaft  governor?     Of  sluggishness? 
Of  racing?     Give  one  remedy  for  each. 

16.  What  is  the  most  common  source  of  trouble  with  shaft  governors?     How  may  this 
trouble  be  located  in  the  various  parts  of  the  governor  mechanism? 

17.  What  lubricant  is  satisfactory  for  governor  roller  bearings?     For  smaller  governor 
pivots? 

18.  How  may  data  be  obtained,  in  steam-engine-driven  electric-power  generating 
stations,  for  governor  adjustment? 

19.  What  causes  a  governor  to  hammer  against  the  stops  when  starting  or  stopping? 
How  may  this  trouble  be  sometimes  corrected  in  a  Rites  governor? 

20.  Explain  by  a  sketch  the  effects  of  shifting  weights  from  one  part  of  a  Rites  gov- 
ernor to  another. 

21.  Name  two  adjustments  of  the  Robb-Armstrong-Sewet  governor. 

22.  Name  three  adjustments  of  the  Fleming  governor. 

23.  What  is  the  advantage  of  the  spring  arrangement  of  the  American-Ball  engine 
governor?    How  may  this  arrangement  be  used  to  vary  the  sensitiveness  of  the  governor? 

24.  Explain  the  action  of  the  auxiliary  springs  of  the  Buckeye  governor.     What  is  the 
bad  effect  if  they  are  too  weak?     What  if  they  are  too  strong?     How  may  their  effective 
strength  be  increased? 

25.  What  is  the  governor  case  of  a  Fitchburg  engine?     Explain  how  to  set  the  governor 
case  on  the  shaft. 

26.  Explain  a  simple  method  of  setting  the  slide  valve  of  an  automatic  engine. 


17 


DIVISION  8 
COMPOUND  AND  MULTI-EXPANSION  ENGINES 

271.  Compound  And  Multi-Expansion  Engines  (Fig.  325) 
are  widely  used  where  the  nature  of  the  load  requires  the  use  of 
reciprocating  engines  and  where  better  economies  are  desired 
than  can  be  obtained  with  simple  engines.     Compound  engines 
range  in   capacity  mainly  from  50  to  4,000  h.p.     For  mar- 
ine service  and  for  driving  machinery  in  mills,  compound 
and  multi-expansion  engines  find  extensive  application.     For 
electric  power  generation,  the  turbine  is  gradually  replacing 
the  compound  engine  because  of  the  turbine's  lower  first  cost 
and  more  compact  form;  and,  under  many  conditions  (Sec. 
299),  its  better  economies.     Also  the  use  of  the  turbine  for 
marine  service  is  increasing.     Where  fuel  is  very  cheap,  as  in  a 
saw-mill,  or  where  there  is  use  for  the  exhaust  steam  for  heat- 
ing or  industrial  purposes,  a  simple  engine  is  usually  preferred 
to  a  compound  one  because  of  its  lower  first  cost;  the  economy 
of  the  engine  then  being  a  secondary  consideration. 

NOTE. — FOR  DEFINITION  OF  THE  COMPOUND  ENGINE  and  classification 
with  respect  to  cylinder  arrangement,  see  Sees.  34  to  40. 

272.  The   Compound   Engine   Usually   Operates   Through 
Large  Temperature  And  Pressure  Ranges. — The  temperature 
or  pressure  range  of  an  engine  is  understood  to  mean  the  differ- 
ence between  the  highest  and  lowest  temperatures  or  pressures 
of  the  steam  within  the  engine  cylinders.     Compound  engines 
are  commonly  operated  condensing  at  150  to  200  Ib.  per  sq. 
in.  boiler  pressure  and  sometimes,  if  the  valves  are  properly 
designed,  on  superheated  steam.     Nothing  is  gained  by  using 
a  compound  engine  for  service  where  the  temperature  and 
pressure  range  is  small.     That  is,  for  a  boiler  pressure  of  100 
Ib.  per  sq.  in.  and  a  back  pressure  of  5  Ib.  per  sq.  in.  gage,  the 
economies  of  the  simple  and  compound  engines  would  be  so 

258 


SEC.  272] 


COMPOUND  ENGINES 


259 


260    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  8 

nearly  equal  that  the  additional  first  cost  of  the  compound 
engine  would,  probably,  not  be  justified.  "In  general" 
(Gebhardt),  "compounding  increases  the  steam  economy  at 
rated  load  10  to  25  per  cent,  for  non-condensing  and  from  15  to 
40  per  cent,  for  condensing  operation."  At  fractional  loads 
the  saving  in  steam  due  to  compounding  is  smaller;  in  fact, 
a  compound  engine  may,  at  light  load,  use  more  steam  than  a 
simple  engine  would  use  at  the  same  load. 

NOTE. — THE  SAVING  SHOWN  BY  THE  COMPOUND  ENGINE  OVER  THE 
SIMPLE  ENGINE  Is  GREATER  AT  HIGHER  BOILER  PRESSURES.  A  certain 
triple  expansion  condensing  engine  is  credited  with  a  consumption  of  but 
11.23  Ib.  of  saturated  steam  per  i.h.p.  hr.  at  257  Ib.  per  sq.  in.  pressure; 
whereas  the  consumption  of  simple  non-condensing,  single-valve  engines 
is  usually  about  30  to  35  Ib.  of  steam  per  i.h.p.  hr. 

273.  The  Principal  Advantages  Of  The  Compound  Or 
Multi -Expansion  Engine  Over  The  Simple  Engine  having  the 
same  total  ratio  of  expansion  (see  note  below)  and  power  out- 
put may  be  enumerated  as  follows;  each  is  discussed  in  a 
succeeding  section:  (1)  Reduced  cylinder  condensation  because 
of  the  lesser  temperature  range  in  each  cylinder  (Sec.  274). 
(2)  Reduced  leakage  loss  partly  due  to  the  lesser  pressure  differ- 
ence in  the  two  ends  or  each  cylinder.  That  is,  the  "net 
pressure"  on  each  piston  is  reduced  by  compounding  (Sec. 
275).  (3)  Higher  mechanical  efficiency  because  the  ratio  of  the 
maximum  to  the  mean  effective  pressure  in  each  of  the  cylin- 
ders is  greatly  reduced.  This  ratio  is  usually  from  40  to  70 
per  cent,  of  what  it  would  be  vvere  the  same  total  ratio  of 
expansion  employed  in  a  simple  engine  (Sec.  276).  (4)  More 
even  torque  when  cross  compound  engines  are  used  with  their 
cranks  set  at  90  deg.  or  120  deg.  apart  (Sec.  277).  The 
important  disadvantages  of  the  compound  or  multi-expansion 
engine  are  its  greater  first  cost,  its  greater  complexity  and  the 
large  amount  of  room  which  it  requires. 

NOTE. — THE  RATIO  OF  EXPANSION  is  the  final  volume  of  the  steam  at 
release  divided  by  its  original  volume  at  cut-off.  In  a  compound  engine, 
the  final  volume  at  release  is  in  the  low-pressure  cylinder  and  the  original 
volume  at  cut-off  is  in  the  high-pressure  cylinder. 

NOTE. — TORQUE  is  the  stress  on  a  body  which  tends  to  cause  it  or 
causes  it  to  turn.  Torque  is  conveniently  measured  in  pound  inches. 


SEC.  274]  COMPOUND  ENGINES  261 

A  pound  inch  of  torque  is  exerted  by  a  force  of  one  pound  acting  at  a 
radius  of  one  inch.  The  torque  exerted  in  Fig.  326  by  the  connecting  rod 
on  the  crank  shaft  is  500  X  14  =  7,000  Ib.  in. 

EXAMPLE. — Assume  that  a  compound  engine  has  a  high-pressure 
cylinder  clearance  of  6  per  cent,  and  a  displacement  volume  of  2.9  cu.  ft., 
and  cuts  off  at  0.32  of  its  stroke.  The  low-pressure  cylinder  has  a  dis- 
placement and  clearance  volume  of  11.8  cu.  ft.  total.  What  is  the  ratio 
of  expansion?  The  boiler  pressure  is  176  Ib.  per  sq.  in.  abs.  Assuming 
that  release  occurs  at  the  end  of  the  stroke  what  is  the  pressure  at  release 
in  the  low-pressure  cylinder?  Assume 
that  the  .expansion  is  hyperbolic — that 
is,  the  absolute  pressure  varies  inversely 
as  the  volume. 

SOLUTION. — The  volume  of  the  steam 
at  cut-off  is  0.32  of  the  displacement 
volume  plus  the  clearance.  That  is, 
(0.32  X  2.9)  +  (0.06  X  2.9)  =  1.103  cu. 
ft.  Then  the  ratio  of  expansion  =  11.8 
-7-  1.102  =  10.7.  If  the  absolute  pres- 
sure varies  inversely  as  the  volume,  the  FIG.  326.— Illustrating  torque  or 
final  pressure  at  10.7  times  the  original  turnins  moment  exerted  in  an  en- 
volume  is  176  +  10.7  =  16.4  Ib.  per  sq. 

in.  abs.  The  final  pressure  at  release  is  always  somewhat  different  in 
practice  than  the  value  thus  calculated. 

274.  How  The  Compound  Engine  Avoids  Excessive  Cylinder 
Condensation  When  Employing  Large  Temperature  And 
Pressure  Ranges  may  be  understood  by  reference  to  Figs.  327, 
328  and  329.  The  phenomena  of  cylinder  condensation  is 
described  below.  As  explained  in  the  author's  PRACTICAL 
HEAT  under  "Gas  And  Vapor  Cycles,"  the  larger  the  steam 
temperature  and  pressure  range  through  which  the  engine 
operates,  the  greater  will  be  its  possible  thermal  efficiency 
provided  the  steam  is  used  economically.  But,  if  a  simple 
single-valve  engine  were  used  with  a  large  temperature  range, 
there  would  be  so  much  cylinder  condensation  that  the  high 
possible  efficiency  would  not  be  even  approximately  realized. 
If  an  engine  cylinder  is  properly  lagged  (insulated),  there  is 
little  cylinder  condensation  due  to  radiation — it  is  nearly  all 
due  to  the  behavior  of  the  steam  during  the  stroke  as  explained 
below. 

EXPLANATION. — In  the  single-valve  engine  (Fig.  327)  the  steam  ports, 
H,  are  alternately  filled  with  live  steam  and  exhaust  steam.  (The 


262    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  8 


following  temperatures  are  taken  from  a  steam  table.)     The  exhaust 
steam  at  120  deg.  fahr. — 26.5  in.  of  mercury  vacuum — must  pass  out 

Live  Steam  Is  Coo  led  Through  Slide" 
Valve  Wa/f  By  Exhaust  Steam 
Steani      Live  Steam  Leaks 
•  Jnfef         [Directly  Into  Exhaust 


-y^A^  Exhaust:^ 
'-Piston.'  ";.. ^/ £ '•?.. t ' 


Some  High -Temperature 
5team  Remains  In  '-" 
Exhaust  Ports '".,-'•  -" 


'So/???  Exhaust  Steam  Left 

In  The  Clearance  Space         ! 


Temperature  Range  =  3 58°- 1 20"  =  238" 

FIG.  327. — Showing  live  steam  and  exhaust  steam  in  contact  with  parts  of  a  single- 
valve  engine.  (The  engine  is  assumed  to  operate  condensing  at  150  Ib.  per  sq.  in.  and 
26.5  in.  of  mercury  vacuum.) 

through  the  same  ports  through  which  the  live  steam  enters  at  358  deg. 
fahr. — 135  Ib.  per  sq.  in.  gage  pressure.     It  is  evident  that  the  walls  of 


Steam  Inlet- 
Cylinder  Wall  Being 
Heated  By  Live  Steam 


Cylinder  Wall  Being 
Coo/ed  By  Exhaust  Steam 


Exhaust    , 

'-Exhaust  Va/ve  °f>en 

Temperature  Range  =  358°- 120°=  236° 

FIG.  328. — Showing  live  steam  and  exhaust  steam  in  contact  with  cylinder  walls  in  a 
simple  four-valve  engine. 

the  ports  as  well  as  those  of  the  cylinder  are  alternately  heated  and  cooled. 
They  are  heated  by  the  live  steam  which  then  condenses  on  them,  and 
cooled  by  the  re-evaporation  of  this  condensed  steam  when  the  pressure 


SEC.  274] 


COMPOUND  ENGINES 


263 


is  lowered.  Some  of  the  steam,  by  thus  condensing  and  re-evaporating- 
passes  through  the  cylinder  without  doing  work.  In  the  simple  four- 
valve  engine  (Fig.  328),  the  steam  alternately  heats  and  c'ools  the  cylinder 
walls  but  the  valves  and  ports  remain  at  a  fairly  constant  temperature. 
Thus  the  four-valve  engine  avoids  some  of  the  cylinder  condensation 
which  takes  place  in  the  single-valve  engine  because  the  steam  passages 
and  the  valves  themselves  are  not  heated  and  cooled.  Furthermore,  the 
exhaust  steam  in  the  clearance  space  of  the  simple  engines  of  Figs.  327 
and  328  mixes  with  the  incoming  live  steam,  and  thus,  condenses  a  portion 
of  the  live  steam. 

In  the  compound  engine  (Fig.  329),  the  exhaust  from  the  low-pressure 
cylinder,  L,  does  not  come  in  contact  at  all  with  the  same  parts  as  does  the 
live  steam  (at  boiler  pressure) .  There  is,  nevertheless,  some  cylinder  con- 
densation in  the  compound  engine  due  to  the  temperature  difference 


Steam 
Supply  - .  .j     150  Ib.  per 


_.  Low-  Pressure  - 
•"    Cylinder      „ 


25 1  b.  per 
sq./rt.  abs.'' 

Temperature  Range 
358"- 241  "=117° 


Fine*/ Exhaust-'      *'"/•? '/A per  scj.  In.  abs. 


Tempera'ture  Range  = 
240°-  120°=  120° 


FIG.  329. — Showing    temperatures   in    various    parts    of    a    compound    engine.     (The 
arrangement  shown  is,  in  general,  that  of  a  Woolf-tandem  compound  engine.) 


between  the  incoming  and  issuing  steam  in  each  cylinder.  But,  because 
of  the  lower  temperature  range  in  each  cylinder,  the  total  condensation 
is  considerably  less  in  the  compound  engine  than  in  either  the  single-  or 
four-valve  simple  engine.  It  will  therefore  be  evident  from  a  study  of  the 
above  explanation  and  of  Figs.  327  to  329  that  compounding  reduces  the 
temperature  range  in  each  compound-engine  cylinder  to  approximately 
one-half  of  that  of  a  simple  engine  in  which  the  total  temperature  range  is 
the  same.  Similar  reasoning  will  disclose  how  the  temperature  range  per 
cyliner  may  be  further  reduced  by  employing  three  or  four  cylinders  as  is 
done  in  triple-  or  quadruple-expansion  engines.  With  a  reduction  in  the 
temperature  range  per  cylinder,  the  total  cylinder  condensation  is  reduced 
correspondingly. 

NOTE. — THE  SURFACES  OF  THE   ENGINE   CYLINDER  WITH  WHICH 
STEAM,  AT  VARIOUS  TEMPERATURES,   CONTACTS  assume,  at  different 


264     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE      [Div.  8 

instants,  very  nearly  the  temperature  of  the  steam  at  those  instants. 
When  a  change  in  steam  temperature  occurs,  the  depth  to  which  such  a 
change  in  temperature  will  penetrate  the  cylinder  walls  will  be  propor- 
tional to  the  time  during  which  the  walls  are  exposed  to  the  steam  at  the 
new  temperature.  Thus,  if  a  steam  stroke  is  performed  in  less  time, 
there  will  be  less  cylinder  condensation.  Therefore,  the  losses  due  to 
cylinder  condensation  decrease  as  the  engine  speed  increases.  Attempts 
have  been  made  to  line  cylinder  heads  with  low-heat-conducting  materials 
to  prevent  cylinder  condensation.  These  materials  have  all  proved  to  be 
of  insufficient  mechanical  strength  and,  therefore,  have  not  been  widely 
used. 

275.  Why  Leakage  Past  The  Piston  And  Valves  Is  Less  In 
A  Compound  Engine  Than  In  An  Equivalent  Simple  Engine 
may  be  understood  by  referring  to  Figs.  328  and  329.     The 
maximum  difference  between  the  pressures  on  the  two  sides  of 
the  piston  and  valves  in  the  high-pressure  cylinder  (Fig.  329) 
is  150  —  25  =  125  Ib.  per  sq.  in.;  and,  in  the  low-pressure 
cylinder   the    difference    is   25  —  1.7  =  23.3    Ib.   per   sq.    in. 
Now,  in  the  simple  engine  (Fig.  328)  the  pressure  difference  is 
150  —  1.7  =  148.3  Ib.  per  sq.  in.     The  pressure  difference  is 
not  much  less  in  the  high-pressure  cylinder  than  it  is  in  the 
simple  engine,  but  the  high-pressure  cylinder  is  much  smaller 
for  the  same  power  output  and  the  volume  of  leakage  is  there- 
fore   correspondingly    small.     Also    the    steam    which   leaks 
past  the  high-pressure  piston  is  effective  in  doing  work  in  the 
low-pressure  cylinder. 

276.  The  Mechanical  Efficiency  Of  A  Compound  Engine 
Is  Ordinarily  Greater  Than  That  Of  An  Equivalent  Simple 
Engine  in  spite  of  the  greater  number  of  bearings  and  moving 
parts  of  the  compound  engine.     The  simple  engine,  to  obtain 
the  same  total  ratio  of  expansion  as  the  compound  engine, 
must  cut  off  earlier  in  its  stroke.     Fig.  330  shows  theoretical 
engine  indicator  diagrams.     /  shows  the  simple  engine  diagram. 
II  shows  the  combined  diagrams  (Sec.  281)  from  the  highl- 
and low-pressure  cylinders  of  a  compound  engine.     The  mean 
effective  pressures  P2  and  P3  in  the  compound-engine  cylinders 
are  large  fractions  of  the  corresponding  maximum  pressures 
in  the  two  cylinders.     In  the  simple  engine,  the  mean  effective 
pressure  Pi  is  only  a  small  part  of  the  maximum  pressure,  PQ. 
The  two  diagrams  show  the  same  total  ratio  of  expansion  but 


SEC.  277] 


COMPOUND  ENGINES 


265 


the  ratio  of  expansion  (see  example  under  Sec.  273)  in  the 
simple  engine  is  15  whereas  that  in  the  compound-engine 
high-pressure  cylinder  is  only  5.  That  is,  the  engine  would  do 
the  maximum  work  for  which  it  was  designed  during  only 
about  }{$  of  the  stroke  in  the  simple  engine  and  for  J£  of  the 
stroke  in  the  compound  engine.  The  low-pressure  cylinder, 
due  to  its  later  cut-off,  does  its  maximum  amount  of  work 
during  half  of  its  stroke.  This  better  distribution  of  the  driving 
force  results  in  better  mechanical  efficiency. 


Zero  Vo/ume  Or  \ 
Clearance  Line  •  \ 


Receiver 
Pressure -..% 

Atmospheric 
L_  -^  ;  Pressure 

Total 
Vacuum^ 

a±r" 


High-Pressure  Cylinder 


\ ^  .'Mean  Effective  Pressure 


;*•'      High-Pressure 
;' Terminal  Drop 
\     Low-Pressure  Cylinder 
}    Mean  Effective  Pressure 


^ 


I-  Simple  Engine  Diagram 
FIG.  330. — Ideal  indicator  diagrams  of  compound  engine  and  equivalent  simple  engine. 


-  Combined  Diagrams  Of 
Compound  Engine 


277.  How  The  Turning  Moment  Or  Torque  Is  Made  More 
Even  In  Compound  Engines  Of  Different  Designs  may  be 
seen  by  referring  to  Figs.  331  to  333.  The  turning  moment  of 
a  tandem-compound  engine  (Fig.  331)  is  only  little  more  even 
or  regular  than  that  of  an  equivalent  simple  engine,  although 
the  later  cut-off  of  the  compound  engine  gives  a  longer  maxi- 
mum turning  moment.  The  torque  developed  by  such  an 
engine  is  shown  graphically  in  Fig.  331.  But,  if  the  high  and 
low-pressure  cylinders  operate  cranks  at  90  deg.  with  each 
other  (as  is  common  in  cross-compound  engines)  the  points 
of  maximum  torque  in  the  two  cylinders  will  occur  90  deg. 
apart  as  shown  in  Fig.  332.  The  driving  moment  on  the  shaft 
will  then  be  much  more  regular  and  the  necessary  flywheel 
size  will  thus  be  greatly  reduced.  If  a  triple-expansion 
engine  has  its  three  cranks  set  at  120  deg.,  the  resulting  torque 


266    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  8 


45°  90°  135°          180°         225"         210" 

Angular    Position    Of  Crank 


315° 


360° 


FIG.  331. — Graph  showing  variation  of  torque  with  angular  position  of  crank  for 
tandem-compound  engine. 


High-Pressure  Dead  Centers -> 


45°  90°  135"          180"         225° 

Angular  Position    Of    Crank 


210° 


315°       360° 


FIG.  332. — Graph  showing  variation  in  torque  with  angular  position  of  crank  in  a  cross- 
compound  engine  with  cranks  at  90  deg. 


.  -  -  -High- Pressure  Deaa"  Centers  - 


\ 


/ 


_ 


-Mean  Torque 


\ 


-High -Press. 


\ 


Cu 


0        30"      GO0     90°      120"     150°     180°     210°     240°   270°    300°    330°    360° 
Angular    Position    Of    Crank 

FIG.  333j — Graph  showing  variation  of  torque  with  angular  position  of  cranks  of  a 
triple-expansion  engine  having  three  cranks  set  at  120  deg. 


SEC.  278] 


COMPOUND  ENGINES 


267 


graph  will  be  that  shown  in  Fig.  333.     An  almost  uniform 
turning  moment  will  result. 

278.  Compound  Engines  May  Be  Classified  With  Respect 
To  The  Method  Of  Transfer  Of  Steam  From  One  Cylinder 
To  Another  as  follows:  (1)  Woolf -compound  engines  (Fig.  334) 
in  which  the  high-pressure  cylinder  exhausts  directly  into  the 
low-pressure  cylinder.  The  cylinders  of  engines  of  this  class 
are  usually  arranged  in  tandem  (Fig.  329)  but  may  also  have 
separate  cranks  set  at  an  angle  of  180  deg.  as  in  Fig.  334. 
(2)  Receiver-compound  engines  (Fig.  335)  in  which  the  steam  is 


Fia.  334. — Woolf-compound  marine  engine.  The  high-pressure  cylinder  exhausts 
directly  through  the  piston  valve  into  the  low-pressure  cylinder.  (For  complete  details 
of  this  engine  see  Fig.  524.) 

delivered  from  the  high-pressure  cylinder  to  a  receiver  and 
thence  to  the  low-pressure  cylinder.  All  cross-compound 
engines  having  cranks  at  90  deg.  and  triple-expansion  engines 
with  cranks  at  120  deg.  are  of  the  receiver-compound  type. 
The  reason  for  this  is  that,  with  these  cylinder  arrangements, 
the  high-pressure  cylinder  does  not  exhaust  at  the  proper 
time  to  supply  the  low-pressure  cylinder  with  steam.  A 
receiver,  A,  Figs.  335  and  336,  is  therefore  employed  to  store, 
during  the  intervals  between  events,  the  steam  from  the  high- 
pressure  cylinder  so  that  it  will  be  available  for  supplying  the 
low-pressure  cylinder.  The  receiver  may  be  in  the  form  of  a 


268     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div. 

i        i    .  ~ T]  -  500  /6v.,  60-Cycle 

Flywheel -  -->^  \\    ^^     ,,-T'     Alternator 


Regular 
Governor 
Small 
Safety  Valve' 


•17-6  C.ToC.- 
I-Plan  View 


2-6 


f 


Receiver-*. 


--9-0' 


•Exhaust  To 
Condenser 


9-0" 


Safety 
Valve 


n-End   Elevation 

FIQ.  335. — Fulton  Iron  Works  Co.  cross-compound,  18  and  36  by  48  in.  engine 
driving  alternator.  (Steam  is  admitted  to  the  high-pressure  cylinder  at  B.  Jt  is 
exhausted  through  C  to  A  where  it  is  reheated.  Thence  it  flows  through  D  to  G  and  is 
exhausted  through  //  to  the  condenser.  The  speed  governor,  N,  is  mounted  on  the  low- 
pressure  cylinder,  and  controls  the  valves  of  both  cylinders  by  means  of  rods,  R  and  S. 
The  over-speed  governor,  M ,  prevents  the  high-pressure  valves  from  picking  up  when  the 
engine  speed  exceeds  a  pre-determined  value.) 


SEC.  279] 


COMPOUND  ENGINES 


269 


separate  chamber  or  it  may  be  merely  an  enlarged  pipe  con- 
necting the  cylinders  or  an  enlarged  low-pressure  steam  chest. 


•Steam  Outlet 
•*••  To  Low-Pressure 
Cylinder 


Manhole 
Cover- 


FIG.  336. — Diagram  of  a  combined  live- 
steam  reheater  and  receiver  for  a  18  and  32 
by  42  in.  cross-compound  engine.  (Fulton 
Iron  Works  Co.  design.  This  corresponds 
to  receiver,  A,  Fig.  335.) 


NOTE. — THE  VOLUME  OF  A  RE- 
CEIVER should  be  at  least  1  to  1.5 
times  the  high-pressure  cylinder 
volume  for  a  cross-compound 
engine  with  cranks  at  90  deg. 
Receivers  having  volumes  of  5  or 
more  times  that  of  the  high-pres- 
sure cylinder  are  sometimes  used. 
For  other  cylinder  arrangements, 
the  receiver  may  be  smaller. 
Small  receiver  volumes  result  in 
irregular  high-pressure  exhaust 
lines,  such  as  those  shown  at  AB 
in  Figs.  337  and  338.  Receivers 
should  be  provided  with  pop 
safety  valves  to  prevent  damage  in 
case  the  receiver  pressure  rises  due 
to  a  failure  of  the  low-pressure 
admission  valves  to  function  prop- 
erly. A  drain  (S,  Fig.  339)  should 
always  be  provided  from  every 
receiver  to  remove  condensed 
steam.  The  pressure  gage  used  on 
a  receiver  should  be  of  the  com- 
pound or  combination  type  and 
should  read  vacuum  and  pressure 
as  high  as  the  boiler  pressure.  A 
by-pass  should  be  provided  for 
admitting  live  steam  to  the  com- 
pound-engine receiver.  This 
assures  that,  if  the  high-pressure 
crank  is  on  dead  center,  the  low- 
pressure  cylinder  may  be  used  to 
start  the  engine.  The  by-pass  also 
permits  "  warming  up  "  the  receiver 
and  low-pressure  cylinder  before 
starting  the  engine. 


279.  Reheaters  Or  Interheaters  (Fig.  336)  are  frequently 
used  with  compound  and  usually  with  triple-expansion 
engines.  A  reheater  or  interheater  is  a  device  for  heating  the 
steam  which  is  discharged  from  the  high-pressure  or  inter- 
mediate cylinder  of  an  engine  before  it  enters  the  next  lower- 


270     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  8 

pressure  cylinder.  Reheaters  are  usually  built  in  the  receiver 
or  take  the  place  of  the  receiver.  The  heating  may  be  done 
with  live  steam  or  with  furnace  gases.  With  compound 


Variable 

iure  X       Receiver 

Back  Pressure  Due  \  Pressure 
\JoL.RCu-f-Off 

.Compression 


Practically  No  Receiver  Volume 


FIG.  337. — Actual  indicator  dia- 
grams showing  decrease  in  receiver- 
pressure  in  a  Woolf  tandem-com- 
pound engine  during  high-pressure 
exhaust  stroke. 


Atmospheric 
Line. 


''Increase  Of 

Low  /  Back  Pressure 

Pressure      f  Due  To  Closed 
Low-Pressure  . 


Little  Receiver  Volume       Steam  Valve 


FIG.  338. — Actual  indicator  diagrams  from 
cross-compound  engine  showing  variation  in 
receiver  pressure  during  exhaust. 


engines,  a  reheater  usually  does  not  improve  the  total  thermal 
efficiency  of  the  engine  materially,  where  the  heating  is  done 
with  live  steam,  unless  the  receiver-pressure  steam  is,  by 


Live-Sfeam 
{Supply 


H-PCylinde. 
(130-lb. 


Jacketing-Sfeam 
Pipes"----, 


Trap-' 


FIG.  339. — Arrangement  of  receivers  and  drains  on  a  triple-expansion  pumping 
engine.  (H.  P.  =  high  pressure  cylinder;  I.  P.  =  intermediate  pressure;  L.  P.  =  low 
pressure.  A,  B  and  C  are  cylinder-jacketing  steam  pipes.  D  and  E  carry  live  steam 
for  the  combined  reheaters  and  receivers. 


reheating,  superheated  about  100  deg.  fahr.  or  more.  Re- 
heaters  always  improve  the  quality  of  the  low-pressure  steam 
materially  and  so  make  the  low-pressure  cylinder  easier  to 


SEC.  280]  COMPOUND  ENGINES  271 

operate.  That  is,  with  steam  of  greater  quality,  the  operation 
and  lubrication  are  more  positive.  Reheaters  in  which  furnace 
gases  are  used  increase  engine  economy  considerably.  Such  a 
reheater  is  used  on  the  Buckeye-mobile  (Fig.  395). 

280.  The  Meanings  Of  Various  Terms  Used  In  Connection 
With  Compound  Engines  are  as  follows:  The  cylinder  ratio 
is  the  ratio  of  the  displacement  volume  (Sec.  3)  of  the  low- 
pressure  cylinder  to  that  of  the  high-pressure  cylinder.     Where 
the  stroke  of  the  two  cylinders  is  the  same,  the  cylinder 
ratio  may  be  taken  for  most  purposes  as  the  square  of  the  ratio 
the    diameters.     Thus,  if  the  high-pressure  cylinder  is  10  in. 
in  diameter  and  the  low-pressure  cylinder  is  20  in.  in  diameter, 
the  cylinder  ratio  is  (20/10)2  =  4  or,  as  sometimes  expressed, 
it  is  4  to  1.     In  computing  the  exact  value  of  cylinder  ratio  the 
volume   occupied   by   the   piston   rods   must   be   deducted. 
The  total  ratio  of  expansion  is  the  ratio  of  the  final  volume  of  the 
steam  in  the  low-pressure  cylinder  to  its  volume  at  cut-off  in 
the   high-pressure   cylinder.     Neglecting   clearance   and,   for 
equal  cut-offs  in  the  two  cylinders,  the  total  ratio  of  expansion 
is  the  cylinder  ratio  times  the  reciprocal  of  the  fraction  of 
stroke  completed  at  high-pressure  cut-off.     Thus,  if  cut-off 
occurs  at  ^  stroke  and  the  cylinder  ratio  is  4,  the  total  ratio  of 
expansion  is  4  X  3  =  12.     Free  expansion  is  the  expansion  of 
the  steam  in  the  receiver  and  passages  between  cylinders.     It 
is  measured  by  the  mean  difference  between  the  pressure  along 
the  exhaust  line  of  the  high-pressure  cylinder  and  that  along 
the  admission  line  of  the  low-pressure  cylinder.     Terminal  drop 
is  the  difference  between  the  pressure  in  the  high-pressure 
cylinder  at  release  and  the  average  receiver  pressure. 

NOTE. — THE  CYLINDER  RATIO  IN  COMPOUND  ENGINES  VARIES  FROM 
ABOUT  2  To  1,  To  ABOUT  8  To  1.  With  a  given  percentage  of  cut-off  in 
the  high-pressure  cylinder,  a  larger  cylinder  ratio  results  in  a  larger  termi- 
nal drop.  But  if  a  sufficiently  early  cut-off  and  a  large  cylinder  ratio  are 
used,  the  terminal  drop  may  be  comparatively  small.  The  economy 
of  the  engine  will  then  be  high  but  its  power  output  small  in  proportion 
to  its  weight.  If  a  larger  power  output  is  desired  at  the  expense  of  ec6n- 
omy,  a  later  cut-off  and  smaller  cylinder  ratio  are  employed. 

281.  Two  Indicator  Diagrams  From  Each  Cylinder  Of  A 
Compound    Engine    May    Be    Combined,    if    the    diagrams 


272     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  8 

are  taken  as  specified  in  Sec.  282  to  form  a  single  diagram, 
Fig.  340.  One  purpose  in  so  doing  is  to  see  how  nearly 
the  combined  expansion  lines,  which  are  thus  obtained, 
conform  to  the  ideal  expansion  curve  or  to  the  saturation 
line  PD  (Fig.  340)  for  the  weight  of  steam  which  was  admitted 
to  the  cylinder.  Leaking  exhaust  and  admission  valves  and 
leaking  pistons  may  thus  be  detected  in  the  compound  engine, 
in  the  same  manner  as  explained  in  Div.  3  for  the  simple 
engine.  A  convenient  method  of  combining  diagrams  is,  by 


Pressure  Scale 
Of  Low- Pressure 

Original  High  -  Diagram  -•-'" 

Pressure  Card- . 


w 


FIG.  340. — Method  of  combining  high-pressure  and  low-pressure  diagrams  from  a 
tandem-compound  engine.  H.P.  =  high-pressure  cylinder;  L.P.  =  low-pressure 
cylinder. 


a  graphic  means,  to  increase  the  volume  scale  of  the  low- 
pressure  diagram  to  the  high-pressure-diagram  volume  scale 
and  to  reduce  the  pressure  scale  of  the  high-pressure  diagram 
to  the  low-pressure  diagram  scale.  The  two  diagrams  will 
then  have  the  same  volume  and  pressure  scales.  This 
method  is  explained  below. 

NOTE. — INDICATOR  DIAGRAMS  WHICH  ARE  To  BE  COMBINED  SHOULD 
BE  TAKEN  SIMULTANEOUSLY  AND  WHEN  THE  LOAD  Is  CONSTANT. 
If  the  diagrams  are  taken  simultaneously  with  two  indicators  while  the 


SEC.  281]  COMPOUND  ENGINES  273 

load  is  changing,  then  the  combined  diagrams  may  show  more  steam 
being  delivered  to  the  receiver  than  is  withdrawn  from  it  or  vice  versa. 
Where  this  occurs,  the  analysis  will  be  misleading.  If  the  two  diagrams 
are  taken  with  one  indicator,  care  should  be  taken  to  restore,  while 
taking  the  second  card,  exactly  the  same  conditions  as  obtained  for  the 
first  card.  Furthermore,  the  conditions  should  be  maintained  constant 
for  an  interval  sufficient  to  allow  the  receiver  pressure  to  assume  its 
normal  value  before  either  diagram  is  taken.  Combining  cards  which 
were  taken  under  different  or  under  changing  conditions  is  a  frequent 
source  of  erroneous  conclusions. 

EXPLANATION. — Two  lines,  OX  and  OY  (Fig.  340),  are  drawn  at  right 
angles,  as  shown,  on  a  large  sheet  of  paper.  A  scale  of  pressures  is 
laid  off  on  OY  equal  to  the  spring  scale  of  the  low-pressure  diagram — 
for  example,  20  Ib.  per  in.  The  low-pressure  diagram,  LP,  is  pasted 
as  shown  with  its  clearance  line  (see  example  under  Sec.  108)  coinciding 
with  OY  and  its  total  vacuum  line  with  OX.  Locate  Z,  on  OX,  even  with 
the  end  of  the  diagram.  Draw  WZQ  through  Z  and  any  convenient 
point,  W.  Now  paste  down  the  high-pressure  diagram,  HP,  as  shown, 
so  that  its  clearance  line  falls  on  OY  and  that  its  highest  point,  K,  is 
correctly  located  on  the  spring  scale  of  the  low-pressure  diagram.  Draw 
RC  as  shown.  Select  point  T  so  that  OT  -f-  OZ  =  (the  displacement 
volume  of  the  low-pressure  cylinder  and  its  clearance}  -5-  (the  displacement 
volume  of  the  high-pressure  cylinder  and  its  clearance]  or,  if  the  percentage 
clearances  in  both  cylinders  are  the  same,  then  OT  -T-  OZ  =  the  cylinder 
ratio.  Draw  TB  at  right  angles  to  OX  to  intersect  WQ.  Draw  BA 
through  B  parallel  to  OX.  Then  as  many  points  as  desired  may  be 
transferred  to  locate  the  new  low-pressure  diagram:  Thus,  to  transfer 
point  M,  draw  MMi,  draw  WMiM2  and  project  M  and  M2  to  Ms', 
Ms  is  the  required  point. 

Draw,  if  not  already  drawn,  the  atmospheric  lines,  RS  and  RiSi. 
Draw  SiRV  and  project  K  to  V.  Then  to  transfer  any  point,  N,  draw 
NNi  and  draw  VNiN*  and  project  N  and  7V2  to  Ns.  N3  is  the  required 
point  on  the  new  high-pressure  diagram. 

To  draw  the  saturation  curve,  calculate  from  test  results  the  weight 
of  steam  used  per  stroke  at  the  load  at  which  the  diagrams  were  taken. 
That  is :  Weight  of  steam  per  stroke  =  (weight  of  steam  used  during  test)  -T- 
(number  of  strokes  during  test).  Add  to  this  weight,  the  weight  of  steam 
trapped  at  compression  in  the  high-pressure  cylinder,  assuming  the  steam 
to  be  dry.  Then  find,  by  using  a  steam  table,  the  volumes  occupied  by 
this  total  weight  of  saturated  steam  at  various  pressures  and  plot  the 
volumes  and  corresponding  pressures  on  the  diagram. 

NOTE. — THE  LOW-PRESSURE  EXPANSION  LINE  OF  A  COMBINED 
INDICATOR  DIAGRAM  is  nearly  always  farther — measured  horizontally  or 
along  the  volume  axis — from  the  saturation  graph  than  is  the  high- 
pressure  expansion  line.  This  is  partly  due  to  the  fact  that  steam  is  pres- 
ent in  the  high-pressure  cylinder  which  is  not  discharged  to  the  receiver 
but  is  retained  as  cushion  steam.  If,  now,  the  weight  of  steam  retained 
18 


274     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  8 

in  the  low-pressure  cylinder  as  cushion  steam  were  the  same  as  that 
retained  in  the  high-pressure  cylinder,  the  two  expansion  lines  might 
follow  one  smooth  curve.  But,  since  the  weight  of  steam  retained  in  the 
low-pressure  cylinder  is  less  than  that  retained  in  the  high-pressure  cylin- 
der, the  total  weight  of  steam  in  the  low-pressure  cylinder  is  less  than  in 
the  high-pressure  cylinder.  Therefore,  its  volume  will  be  less.  That 
the  low  pressure  expansion  line  is  farther  from  the  saturation  graph  than 
is  the  high-pressure  expansion  line  is  also  because  part  of  the  steam  is 
condensed  in  the  high-pressure  cylinder  and  upon  being  admitted  to  the 
low-pressure  cylinder  still  more  of  it  is  condensed.  When  an  interheater 
or  reheater  (Sec.  279)  is  used,  the  low-pressure  expansion  line  is  much 
nearer  the  saturation  graph.  Giving  the  low-pressure  cylinder  later 
cut-off  does  not,  as  might  be  expected,  extend  the  low-pressure  expansion 
line.  This  is  because  giving  later  cut-off  in  the  low-pressure  cylinder  gives 
a  lower  receiver  pressure. 

NOTE. — COMPOUND-ENGINE  INDICATOR  CARDS  MAY  ALSO  BE  COM- 
BINED To  SHOW  THE  SIMULTANEOUS  CONDITIONS  IN  BOTH  CYLINDERS 
as  suggested  in  Figs.  337  and  338.  For  this  purpose  the  volume — hori- 
zontal— scales  need  not  be  changed.  The  pressure  scales  are  replotted 
to  a  common  scale  and  the  simultaneous  events  for  each  card  are  plotted 
above  one  another  vertically.  The  line  AB  shows  the  receiver  pressure. 
The  line  CD  shows  the  pressure  of  the  steam  as  admitted  to  the  low- 
pressure  cylinder.  The  vertical  distance  at  any  point  between  AB  and 
CD  shows  the  pressure  drop  through  the  receiver.  Hence,  such  cards  are 
useful  in  studying  receiver  pressures  and  drop. 

282.  A  "Mean  Indicator  Diagram"  Must  Be  Drawn,  If 
Unlike  Indicator  Diagrams  Are  Obtained  From  The  Head 
And  Crank  Ends  Of  Either  Engine  Cylinder,  before  the  dia- 
grams from  the  two  cylinders  can,  properly,  be  combined.  This 
is  because  some  of  the  steam  which  passed  through  the  crank 
end  of  the  high-pressure  cylinder  will  pass  through  the  head 
end  of  the  low-pressure  cylinder  if  the  valves  are  not  adjusted 
symmetrically  as  shown  by  a  balanced  indicator  card.  A 
graphic  method  of  drawing  a  mean  card  for  an  engine  cylinder 
is  as  follows : 

EXPLANATION.— The  indicator  diagrams,  7  and  II  (Fig.  341),  are  ruled 
with  vertical  equally  spaced  lines  as  shown.  The  clearance  lines  M 
and  atmospheric  or  total  vacuum  lines  (whichever  is  most  convenient) 
WZ  are  also  drawn.  A  reference  line  XY  is  then  drawn  and  vertical 
lines  are  drawn  as  shown  twice  as  far  apart  as  those  in  /  and  II.  The 
sum  of  the  clearances,  WA  and  CZ,  are  laid  out  at  XA ,  and  the  clearance 
line  XX i  is  drawn.  Now  to  transfer  any  point  5,  and  its  corresponding 


SEC.  283] 


COMPOUND  ENGINES 


275 


point,  D,  to  the  mean  diagram,  lay  out,  with  a  pair  of  dividers  or  other 
means,  the  distance  Ai-Di  equal  to  the  sum  of  AB  and  CD.  It  will  be 
noted  that  both  the  pressure  scale  and  volume  scale  of  the  diagram  are 
doubled  by  this  operation. 


-Head-End 


FIG.  341. — Illustrating  method  of  drawing  a  mean  indicator  diagram  from  head-end 
and  crank-end  indicator  diagrams. 


283.  The  Indicated  Horse  Power  Of  Compound  Engines 

may  be  computed  by  computing  the  power  of  each  cylinder 
and  adding  the  results.  The  method  for  computing  the  horse 
power  of  a  simple  engine  was  explained  in  Sec.  123.  Each 
cylinder  of  a  multi-expansion  engine  may  be  considered  as  a 
simple  engine  in  computing  indicated  horse  power.  The 
cylinder  area,  the  mean  effective  pressure,  and  spring  scale 
are  ordinarily  different  in  the  different  cylinders.  Therefore 
little  is  ordinarily  gained  by  computing  the  power  of  the  two 
cylinders  together.  However,  if  the  diagrams  have  been 
carefully  combined,  as  explained  in  the  preceding  section,  the 
resulting  diagram  may  be  treated  as  a  single  diagram  in 
computing  indicated  horse  power. 


276     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  8 

284.  The   Receiver   Pressure   Usually   Varies    Somewhat 
During    The    Stroke    of    the    engine.     In    Woolf-compound 
engines   (Fig  334)   the  back  pressure   on  the  high-pressure 
cylinder   is   a   maximum   at  high-pressure  release  but  falls 
off  rapidly  due  to  the  fact   that  the  low-pressure-cylinder 
volume  increases  faster  than  the  high-pressure-cylinder  volume 
decreases.     This  effect  is  apparent  in  most  tandem-compound 
engines  but  is  much  less  if  a  receiver  is  used.     The  high- 
pressure  exhaust  line  (AB,  Fig.  338),  which  also  represents  the 
receiver  pressure,  of  a  cross-compound-engine  diagram  usually 
curves  down  at  its  ends  due  to  the  low-pressure  cylinder  admit- 
ting steam  at  the  ends  of  but  not  in  the  middle  of  the  high- 
pressure  stroke. 

285.  With    Compound    Engines,    The    Correct    Receiver 
Pressure  Must  Be  Maintained  To  Insure  Economical  Opera- 
tion.— A   radically  wrong  receiver  pressure  causes   most  of 
the  work  to  be  done  in  one  cylinder  and  the  engine  then  gives 
little   better  economies  than  would   a  simple  engine.     But 
even  when  the  receiver  pressure  is  varied  within  apparently 
reasonable  limits,  there  may  be  a  difference  of  10  per  cent, 
or  more  in  the  steam  consumed  by  the  engine  per  indicated 
horse  power  hour  due  to  these  receiver  pressure  differences. 
The   receiver  pressure   recommended  by   one  manufacturer 
for  non-condensing  compound  engines  is  about  30  Ib.  per  sq. 
in.  gage  and  for  condensing  operation,  about  15—20  Ib.  per 
sq.  in.  gage. 

286.  To  Find  The  Best  Receiver  Pressure  For  Any  Receiver- 
Compound   Or   Multi -Expansion  Engine,   find   the   receiver 
pressure  at  which  the  net  work  done  in  the  cylinders  is  equal. 
This   can   be   accomplished   by   taking   successive   indicator 
cards  at  the  same  load  from  each  cylinder  and  varying  the 
receiver  pressure.     Then  the  power  (see  Sec.  123)  developed 
by  each  cylinder  with  each  receiver  pressure  is  determined. 
The  best  receiver  pressure  is,  of  course,  that  at  which  the 
economy  of  the  engine  is  maximum.     But  nearly  all  compound 
engines  are  so  designed  that  the  work  in  the  two  cylinders  is 
about  equal  when  economy  is  maximum.     Therefore,  if  the 
work  done  by  the  several  cylinders  is  equal,  it  may,  ordi- 
narily, be  assumed  that  the  receiver  pressure  is  correct.     In  a 


SEC.  286] 


COMPOUND  ENGINES 


277 


.'Pivot  Is  Stationai 
Vertically 


Baft 
Weight-^ 


Rod  To  High-Pressure 
Valve  Control** 
jrn,  V 


Journal;  . .  • 
Free  To  Turn 
On  Shaft 


Flange  For 
Bo/t/'ng  To 
Frame 


Handwheel 

For  Regulating      }    I . 

Receiver  Pressure 


Governor 
Pulley,^ 


Fio.  342. — Cross-compound  Corliss  engine  governor,  N,  Fig.  335  showing  receiver- 
pressure  regulation  device.  (Fulton  Iron  Works  Co.  design).  This  governor  is  located 
on  the  low-pressure  cylinder  and  controls  the  regular  knock-off  cams  on  both  cylinders. 


278    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  8 


High-pressure          Spindle- 
Valves  Sleeve •--> 

Operated  by  Column  ..-• 
/fc//<w  Rod 


combined  diagram,  the  work  areas  may  be  directly  compared. 
When  it  is  desired  to  establish  as  nearly  as  possible  the  correct 
receiver  pressure  before  taking  indicator  diagrams,  the  rules 
given  in  the  following  section  may  prove  useful. 

287.  The  Receiver  Pressure  For  A  Compound  Engine 
Depends  On  The  Cylinder  Ratio. — For  condensing  operation, 
the  receiver  pressure  should  be  approximately  the  absolute 
boiler  pressure  divided  by  the  cylinder  ratio.  Thus,  if  there 
is  a  steam  supply  pressure  of  185  Ib.  per  sq.  in.  abs.  and  a 
cylinder  ratio  of  5  (5  to  1),  the  receiver  pressure  should  be 
about:  185  -i-  5  =  37  Ib.  per  sq.  in.  abs.  or  about  22  Ib.  per 
sq.  in.  gage.  For  non-condensing  operation,  the  receiver 
pressure  should  be  approximately  the  geometric  mean  between 
the  absolute  steam-supply  pressure  and  the  absolute  back 
pressure.  The  geometric  mean  between  two  values  is  the 

square  root  of  their  product.  Thus, 
if  there  is  a  line  pressure  of  135  and 
a  back  pressure  of  15  Ib.  per  sq.  in. 
abs.,  the  receiver  pressure  should  be: 
A/15  X  135  =  45  Ib.  per  sq.  in.  abs. 
or  about  30  Ib.  per  sq*  in.  gage. 

288.  The  Governor  Gear  Adjust- 
ment (Figs.  342  and  343)  may  be 
used  to  vary  the  receiver^  pressure 
in  those  compound  Corliss  engines 
which  change  the  cut-off  in  both 
cylinders  by  means  of  a  single  gov- 
ernor. If  the  low-pressure-cylinder 
cut-off  is  made  later  relative  to 
J^^l^tL^ZS  that  in  the  high-pressure  cylinder, 
engine  of  Fig.  335.  This  is  view  then  the  receiver  pressure  will  be 
xx,  Fig.  342.  lowered  and  the  low-pressure  cyl- 

inder will  then  do  less  work.  Conversely,  if  the  low-pressure- 
cylinder  cut-off  is  made  earlier  relative  to  that  in  the 
high-pressure  cylinder,  the  receiver  pressure  will  be  raised 
and  the  low-pressure  cylinder  will  do  more  work.  After 
making  any  valve-gear  adjustments,  it  is  well  to  see  whether 
the  receiver  pressure  is  correct.  If  it  is  not  correct,  the 
linkage  between  the  cams  of  the  two  cylinders  should  be 


Handwneet 
For  Regulating 
Receiver  Pressure 


SEC.  289] 


COMPOUND  ENGINES 


279 


adjusted  to  give  the  correct  pressure.  There  will  be  some 
variation  in  receiver  pressure  with  load  with  this  arrangement 
(see  Fig.  344)  but  not  as  much  as  when  only  the  high-pressure 
cylinder  is  governed  (Fig.  345). 

M 

i£ .  -High-Pressure 
Cylinder  Vo/ume 


120 

u  v»   ^ 

«5|05 

I^J^TV\ 
i  »  \ 

Points  Of  High- 
Pressure  Cut-Off 

c 

i  \\ 

.E  90 

\    \ 
\ 

\    i  .-'Htgh-Pressure- 

C*     . 

',     \ 

\.  '       Cylinder  Vo/ume 

u>    /  D 

«,     \ 

*\ 

u 

\     \ 

S.60 

\      \ 

\.--Terminal 

"45 

V 

\     /-'\    /?/~oo 

\       Ns 

tS 

F  c  \ 

vx       x^^ 

in  30 

^''        \ 

Y    X^     *"^"--^  ^--F, 

(O 

I15 

fiT.-rr.-r 

A        A 

ex 

0 

i 

Condenser 

^Points  Of  Low 

°ressure  •  ' 

Pressure  Cut-Off 

^Receiver  Pressure  At 
Pressure-'  Intermediate  Load 

FIQ.  345. — Theoretical  indicator  dia- 
grams showing  effect  of  Governing  high- 
pressure  cylinder  only. 


FIG.  344. — Theoretical  indicator  dia- 
grams showing  variation  in  receiver 
pressure  due  to  cut-off  governing  in  both 
cylinders.  The  lines  FFi,  EE\,  and  AAi 
represent  respectively  the  different  re- 
ceiver pressures. 


289.  Where  Only  The  High-Pressure  Cylinder  Is  Governed, 

the  cut-off  in  the  low-pressure  cylinder  is  fixed.  The  receiver 
pressure  will  then  vary  with  the  load.  The  low-pressure- 
cylinder  cut-off  should  therefore  be  set  at  a  point  which  will 
give  the  proper  receiver  pressure  under  the  average  load 
expected. 

EXPLANATION. — Fig.  345  shows  theoretical  indicator  diagrams  from  a 
compound  engine  which  is  governed  by  changing  the  cut-off  in  the  high- 
pressure  cylinder  only.  The  low-pressure  cut-off  is  fixed  at  LL.  When 
high-pressure  cut-off  is  late  as  at  A,  the  steam  expands  only  to  B  before 
it  attains  the  volume  MM  of  the  high-pressure  cylinder.  This  amount 
of  steam  at  the  cut-off  volume  LL  of  the  low-pressure  cylinder  exerts  a 
pressure  C,  which  is  therefore  the  receiver  pressure  at  this  load.  Simi- 
larly, the  receiver  pressures  P  and  R  are  produced  when  cut-off  occurs  at 
D  and  H.  In  the  diagrams  of  Fig.  344,  cut-off  occurs  at  B,  C,  and  D. 
The  low-pressure  cut-off  is  varied  by  the  governor  so  as  to  occur  at  A\, 
Ei  and  F\.  This  governor  action  varies  the  receiver  pressure  but  little 
and  keeps  the  work  in  the  two  cylinders  about  equal. 


280    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  8 


290.  Triple-  And  Quadruple -Expansion  Engines  Are  Rarely 
Used  In  Stationary  Power  Plants  except  in  large  existing 
pumping  stations.  New  pumping  stations  use  turbine-driven 
centrifugal  pumps  for  large-capacity  pumping  service.  But 
multi-expansion  engines  are  built  extensively  for  marine 
service.  Fig.  346  shows  a  typical  triple-expansion  marine 
engine.  Two  low-pressure  cylinders,  LI  and  L2,  are  used  to 


Low-Pressure 
Cylinder-^ 


Low-Pressure      Relief      Intermediate 
Valve        Cylinder-         'Valve       ^Cylinder 
Chest^  ' 


High-Pressure 
Cylinder 


FIG.  346. — Four-cylinder  triple-expansion  marine  engine. 

secure  proper  mechanical  balance.  The  combined  indicator 
diagrams  from  a  quadruple-expansion  engine  are  shown  in 
Fig.  347. 

291.  To  Set  The  Valves  Of  A  Compound  Engine,  set  the 
valves  of  each  cylinder  separately.  The  high-pressure  valves 
may  be  set  as  explained  for  simple  engines  in  Divs.  4  and  5. 
The  low-pressure  valves  should  be  given  more  lead  than  those 
of  the  high -pressure  cylinder.  About  Jli6  to  %4  in.  per  foot 
of  stroke  is  advisable  for  most  compound-engine  low-pressure 
valves.  For  vertical  engines,  it  is  advisable  to  give  little  more 


SEC.  291] 


COMPOUND  ENGINES 


281 


lead  on  the  bottom  than  on  the  top  of  the  cylinder.  Where 
the  valves  are  very  quick  acting,  it  may  be  more  convenient 
to  set  them  in  relation  to  the  angular  position  which  the  crank 
assumes  at  the  instant  when  the  admission  valve  begins  to  open, 
rather  than  to  set  for  lead.  On  the  low-pressure  cylinder,  the 
valve  should  start  to  open  when  the  crank  is  7  to  10  deg. 
ahead  of  dead  center.  This  angular  lead  may,  however,  be 
as  high  as  15  deg. 


"  ~5feam  Supply  Pressure 


I     f.--HuperJbo/ic 

I1/: '      Expansion  Line 


•Condenser  Pressure 
FIG.  347. — Combined  indicator  diagrams  from  a  quadruple  expansion  engine. 


QUESTIONS  ON  DIVISION  8 

1.  Name  two  conditions  under  which  compound  engines  are  commonly  used. 

2.  Over  what  pressure  ranges  are  compound  engines  commonly  operated?     When  are 
simple  engines  almost  as  economical  as  compound  engines?     What  saving  in  steam  may 
be  expected  from  the  use  of  a  compound  engine  operated  condensing  over  the  steam 
consumption  of  a  simple  condensing  engine? 

3.  Give  the  four  principal  advantages  of  compound  engines. 

4.  Show  by  a  sketch  how  the  live  steam  comes  in  contact  with  the  same  parts  as  does 
the  exhaust  steam  in  a  simple  engine.     Why  does  not  this  occur  in  a  compound  engine? 

5.  How  do  engine  speed  and  the  heat  conductivity  of  the  cylinder  wall  affect  cylinder 
condensation? 

6.  Explain  how  the  loss  due  to  leakage  past  the  cylinder  and  valves  is  lessened  in  a 
compound  engine. 

7.  Why  is  the  mechanical  efficiency  of  a  simple  engine  employing  a  large  ratio  of 
expansion  less  than  that  of  an  equivalent  compound  engine? 

8.  What  is  torque?     How  is  it  measured?     Why  is  the  torque  very  uniform  in  a  triple- 
expansion    engine    with    cranks    at    120  deg.?     Which    do   you  consider  preferable,  a 
tandem-  or  a  cross-compound  engine?     Why? 

9.  How  may  compound  engines  be  classified  with  respect  to  the  steam  flow?     Why  is 
a  receiver  necessary  in  a  cross-compound  engine  with  cranks  set  at  90  deg.  ? 

10.  How  large  should  a  receiver  for  a  cross-compound  engine  be?     With  what  acces- 
sories and  pipes  should  it  be  equipped? 


282    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  8 

11.  What  are  two  principal  kinds  of  reheaters? 

12.  What  is  the  cylinder  ratio  of  a  compound  engine?     What  is  free  expansion? 
Terminal  drop? 

13.  What  cylinder  ratios  are  used  in  compound  engines?     How  is  engine  economy 
affected  by  larger  cylinder  ratios  and  earlier  cut-off?     How  does  this  affect  power 
output? 

14.  Explain  by  a  sketch  how  indicator  diagrams  from  high-  and  low-pressure  cylinders 
of  a  compound  engine  may  be  combined. 

15.  What  causes  the  low-pressure  expansion  line  of  a  combined  indicator  diagram  to 
fall  farther  from  the  saturation  line  than  does  the  high-pressure  expansion  line? 

16.  How  may  the  indicated  horse  power  of  multi-expansion  engines  be  computed? 

17.  Explain  how  the  receiver  pressure  varies  during  a  stroke  in  a  cross-compound 
engine. 

18.  How  may  the  correct  receiver  pressure  for  an  engine  be  determined  by  means  of 
a  steam  engine  indicator? 

19.  Which  method  of  compound-engine  governing  gives  the  greatest  variations  in 
receiver  pressure?     Why? 

20.  How  much  lead  should  there  be  in  the  valves  of  a  low-pressure  cylinder  of  a  com- 
pound engine? 

PROBLEMS  ON  DIVISION  8 

1.  Approximately  what  receiver  pressure  should  a  compound  condensing  engine  have 
when  taking  steam  at  150  Ib.  per  sq.  in.  gage  if  the  cylinder  ratio  is  4. 3:1.     What 
should  be  the  receiver  pressure  for  a  non-condensing  compound  engine  taking  steam  at 
100  Ib.  per  sq.  in.  gage  and  exhausting  at  5  Ib.  per  sq.  in.  gage? 

2.  If  the  crank  arm  in  a  simple  engine  is  6  in.  long  and  the  cylinder  diameter  is  10  in., 
what  maximum  torque  can  the  piston  exert  on  the  shaft  if  the  effective  pressure  on  the 
piston  is  150  Ib.  per  sq.  in.?     Assume  that,  when  the  crank  and  connecting  rod  are  at 
right  angles  to  each  other,  the  force  on  the  crank  pin  is  90  per  cent,  of  that  on  the  piston. 

3.  If,  in  a  quadruple-expansion  engine,  the  temperature  ranges  in  all  cylinders  are 
equal,  and  if  steam  is  supplied  to  the  engine  at  225  Ib.  per  sq.  in.  gage  and  exhausted  into 
a  condenser  where  the  vacuum  is  28.5  in.  of  mercury  column,  what  is  the  temperature 
range  in  each  cylinder?     Barometer  =  30  in. 

4.  A  compound  engine,  which  has  a  cylinder  ratio  of  4.5:  1  cuts  off  at  26  per  cent,  stroke 
in  the  high-pressure  cylinder.     Neglecting  clearance,  what  is  its  ratio  of  expansion?      If 
there  is  6  per  cent,  clearance  in  each  cylinder,  what  is  the  ratio  of  expansion? 

5.  If  a  compound  engine  has  a  stroke  of  5  ft.,  what  lead  should  its  low-pressure 
cylinder  admission  valves  have? 


DIVISION  9 


CONDENSING   AND   NON-CONDENSING  OPERATION 

292.  By  Condensing  Operation  Of  A  Steam  Engine  Is 
Meant  Its  Operation  In  Connection  With  A  Steam  Condenser 
So  That  A  Pressure  Considerably  Below  Atmospheric  Pressure 
Is  Maintained  In  The  Engine  Exhaust  Pipes  And  Passages. 

That  is,  the  back  pressure  on  an  engine  operated  condensing 


Steam  at 
±400  Deg  fahr 


/  95  Deg.  Fahr 
Outlet  'to  Dry  -Air  Pump 
Outlet  to  Condensate  Pump 


/nfe 


FIG.  348.—  Diagram  of  uniflow-engine  cylinder  connected  through  expansion  joint  to 

surface  condenser. 

(Fig.  348)  is  ordinarily  10  to  14  Ib.  per  sq.  in.  below  atmos- 
pheric pressure,  while  that  on  one  operated  non-condensing 
is  usually  0  to  5  Ib.  per  sq.  in.  above  atmospheric  pressure. 

NOTE.  —  A  CONDENSER  Is  A  CHAMBER  WHEREIN  THE  EXHAUST  STEAM 
FROM  THE  ENGINE  Is  COOLED  AND  THEREBY  CONDENSED  INTO  WATER. 
A  partial  vacuum,  into  which  the  engine  (Figs.  349  and  350)  exhausts,  is 
thus  formed.  The  subject  of  condensers  is  treated  quite  fully  in  the 
author's  STEAM  POWER  PLANT  AUXILIARIES  AND  ACCESSORIES. 

283 


284     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  9 


.-Steam-Supply  Pipe 

.-High  -Pressure  Cylinder 

,  Low '-Pressure 
Cylinder 


Surface         Feed-  Water 
(Condenser       Heater 


Discharge^ 
Tunnel    ~ ' 


'Wef-Air      Boiler- Feed,.' 
Pump  Pump  --•' 

Cylinder 
"'""")    Circulating- 
Tunnel     Pump  Cyl-nc!ter 


FIG.  349. — Surface  condenser  connected  for  service  with  tandem-compound  engine. 
Steam  is  discharged  from  low-pressure  cylinder,  L,  through  P.  The  cylinder  oil  and 
water  are  removed  by  S  and  collected  in  R.  The  steam  is  condensed  in  C  by  water, 
which  is  sucked  from  7  by  W  and  discharged  into  D.  The  air  and  condensate  are  re- 
moved by  A,  the  latter  being  heated  in  H  and  fed  back  to  the  boiler  by  F.  (Cochrane 
Heater  Catalogue.) 


Atmospheric 
Relief 


Strainer 


*-Hot  Well 

FIG.  350. — Ejector-jet  condenser  installed  for  service  with  simple  Corliss  engine. 
Schutte  &  Koerting  Co.  catalogue;  water  is  circulated  by  P  through  S  and  the  condenser  C. 
The  velocity  of  the  water  issuing  from  jets  in  C  is  such  that  water  and  air  are  discharged 
from  the  vacuum  in  C  against  atmospheric  pressure.) 


SEC.  293]       CONDENSING  AND  NON-CONDENSING 


285 


293.  The  Main  Purpose  In  Reducing  The  Back  Pressure 
On  A  Steam  Engine  By  Means  Of  A  Condenser  Is  To  Save 
Steam  And  Thus  Save  Coal. — That  is,  an  engine  will  develop 
a  given  amount  of  power  from  less  steam  if  a  condenser  is 
used;  or,  conversely,  it  will  develop  more  power  on  a  given 
amount  of  steam  when  a  condenser  is  used. 

EXPLANATION. — Fig.  351  represents  an  ideal  condensing  engine  indi- 
cator diagram  (Sec.  78)  superimposed  on  a  corresponding  non-condensing 
diagram.  The  steam  pressure  is  represented  by  line  PP';  atmospheric 
pressure  by  line  A  A';  and  zero  pressure  or  complete  vacuum  by  VV. 
Consider  first  that  the  same  volume  of  steam,  S2,  is  used  for  both  con- 
densing and  non-condensing  operation,  and  that  this  steam  expands  as 
represented  by  line  RS.  Then,  area  PRSB'BP  represents  the  work  done 


FIQ.  351. — Ideal  indicator  cards  showing  comparative  work  areas,  working  pressures, 
and  steam  consumptions  for  condensing  and  non-condensing  operation. 


by  the  engine  running  non-condensing;  area  PRSC'CP  represents  that 
done  condensing.  The  shaded  area  represents  the  increased  work  done 
when  running  condensing  over  that  when  running  non-condensing.  PI 
represents  the  working  pressure  range  with  the  condenser  as  compared 
to  Pa  without  it.  The  engine  thus  develops  more  power  from  the  same 
amount  of  steam  when  operated  condensing. 

But  assume  that  by  an  earlier  cut-off  less  steam,  Si,  is  admitted  to 
the  cylinder  so  that  the  expansion  follows  the  new  line  MN.  Si  is 
assumed  to  be  of  such  an  amount  that  the  work  area  PMNC'CP  is  equal 
to  the  area  PRSB'BP.  Then  the  shaded  area  is  equal  to  the  area  MNSR, 
and  the  work  done  by  a  volume  of  steam  Si  with  condensing  operation 
is  equal  to  that  done  by  a  volume  of  steam  £2  with  non-condensing 
operation.  Thus  the  same  amount  of  work  is  done  by  less  steam  with 
condensing  operation. 

NOTE. — METHODS  OF  CALCULATING  THE  PERCENTAGE  SAVING  OR 
POWER  INCREASE  DUE  To  CONDENSING  OPERATION  are  given  in  the 
author's  STEAM  POWER  PLANT  AUXILIARIES  AND  ACCESSORIES. 


286     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE      [Div.  9 

294.  Condensing  Operation  Is  Not  Economical  For  Any 
Engine  When  Most  Of  The  Exhaust  Steam  From  The  Engine 
Can  Be  Profitably  Used  For  Heating  Or  Industrial  Purposes. 
It  is  much  more  economical  to  use  exhaust  steam  for  heating 
than  to  condense  the  exhaust  and  heat  with  live  (boiler- 
pressure)  steam.  When  all  of  the  exhaust  steam  from  an  engine 
is  used  for  heating,  the  engine  merely  acts  as  a  reducing  valve 
and  furnishes  power  as  a  sort  of  by-product.  On  the  other 
hand,  when  the  exhaust  is  condensed,  much  heat  is  absorbed 
by  the  condensing  water  and  is  lost.  In  general,  the  exhaust 
from  an  engine  should  be  condensed  only  when  it  cannot  be 
used. 


Outet  To... 
' 


FIG.  352. — Low-level  jet  condenser  and  condenser  pump  connected  to  engine  and 
cooling  tower.  (Water  is  pumped  by  the  hot-well  pump  from  H  to  the  top  of  T,  and 
flows  by  gravity  to  W.  If  the  condenser,  C,  fails  to  work,  V  opens  and  the  engine 
exhausts  to  the  atmosphere  through  A.  The  heat  absorbed  by  the  water  in  C  is  removed 
by  evaporation  in  T.) 

NOTE. — SINCE  CONDENSING  OPERATION  REQUIRES  CONSIDERABLE 
RELATIVELY  COLD  WATER,  IT  Is  ONLY  FEASIBLE  WHERE  THERE  Is  AN 
ADEQUATE  WATER  SUPPLY.  In  practice  25  to  100  Ib.  of  water  are 
required  for  each  pound  of  steam  condensed.  Water  for  a  condenser 
may  be  recooled  in  a  cooling  tower  (Fig.  352)  or  pond  and  used  repeatedly. 

295.  Table  Showing  Average  Steam  Consumptions  Of 
Various  Types  Of  Engines  Operated  Condensing  And  Non- 
Condensing  At  Full  Load.  (Based  on  data  from  O.  B. 
Goldman's  FINANCIAL  ENGINEERING.) 


SEC.  296]       CONDENSING  AND  NON-CONDENSING 


287 


Engine 

Saturated  steam  at 
150  Ib.  per  sq.  in. 
pressure 

Superheated  steam  at 
the  same  pressure,  100 
deg.  fahr.  superheat 

Pounds  of 
steam  per  i.h.p. 
hr. 

Per 
cent. 

Pounds  of 
steam  per  i.h.p. 
hr. 

Per 
cent. 

Non- 
cond. 

Cond.  * 

Saving 

Non- 
cond. 

Cond.* 

Saving 

Simple,     high-speed,    single-valve, 
18  in.  -stroke 
Simple,  four-valve,  18-in.  stroke.  .  .  . 
Compound  18-in.  stroke  

27.6 

24.1 
22.0 
20.8 

25.7 

19.8 
14.8 
17.1 

7 

18 
33 

18 

17.0 
18.3 

12.7 
15.0 

25 

18 

*  The  condensing  operation  is  at  26  in.  of  mercury  vacuum. 

NOTE. — The  steam  consumptions  of  the  condenser  auxiliaries  are  not 
included  in  the  above  values.  The  condenser  auxiliaries,  when  steam 
driven,  ordinarily  consume  about  1  to  6  per  cent,  as  much  steam  as  is 
consumed  by  the  main  engine. 

296.  Cylinder  Condensation  Is  Of  Importance  In  Determin- 
ing Whether  Condensing  Or  Non-Condensing  Operation  Is  The 
More  Economical. — The  efficiency  loss  due  to  cylinder  con-*- 


60 


3 

£•55 


20 


\$3 


Condenser  Vacuum-?6 In. 
Pressure -150  Lb.  per  Sq.  In,  -  - 


A       10  20  30  40  50     56 

Percentage   of   Stroke    at  Cut-Off 


FIG.  353.  —  Graph  showing  that,  with  condensing  operation  of  a  simple  engine,  the 
loss  due  to  cylinder  condensation  is  greater  than  with  non-condensing  operation;  and 
that  it  increases  as  the  cut-off  becomes  earlier.  (The  percentage  loss  is  greater  in  smaller 
engines.  The  increased  loss  due  to  condensing  operation  is  greater  when  the  steam 
pressure  is  less.  The  values  were  calculated  by  a  formula  by  R.  C.  H.  Heck.) 


densation  (Sec.  307)  in  a  simple  engine  (Figs.  353  and  354)  is 
increased  by  condensing  operation.  The  live  steam  in  a  simple 
engine  is  admitted  to  the  space  which  was  recently  occupied 
by  steam  at  condenser  pressure.  The  live  steam  may  have  a 


288    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  9 

temperature  300  deg.  fahr.  or  more  above  that  of  the  con- 
denser-pressure steam;  see  a  steam  table  for  temperatures  of 
steam  at  different  pressures.  The  live  steam  (as  explained 
in  Sec.  274)  must  heat  the  cylinder  walls  to  nearly  its  own 
temperature.  In  heating  the  cylinder  walls,  the  live  steam  is 
cooled  and  thereby  partially  condensed  which  results  in  a 
heat  loss.  In  compound  engines  (Div.  8),  the  difference  in 


15  20 

Back -Pressure,  Lb.  Per  Sq  In.  Aba. 

FIG.  354. — Graph  showing  that,  as  the  back  pressure  on  a  simple  engine  is  reduced  — 
or  as  the  vacuum  is  increased — the  loss  due  to  cylinder  condensation  becomes  greater. 
(Simple  engine  18  X  12  in.  Steam  pressure  100  Ib.  per  sq.  in.  gage.  Speed  175  r.p.m. 
Cut-off  at  20  per  cent,  stroke.  Calculated  by  a  formula  by  R.  C.  H.  Heck.) 

temperature  between  the  incoming  and  outgoing  steam  in  each 
cylinder  is  usually  much  less  than  in  a  simple  engine.  Uniflow 
engines  (Fig.  348)  are  so  constructed  that  the  cool  condenser- 
pressure  steam  is  exhausted  in  the  center  of  the  cylinder 
whereas  the  live  steam  is  admitted  at  the  ends.  This  prevents, 
in  a  measure,  the  cooling  of  the  cylinder  ends  by  the  exhaust 
steam.  Compound  and  uniflow  engines  are  therefore  able  to 
get  the  benefit  of  the  increased  working  pressure  effected  by  a 
condenser  without  incurring  excessive  loss  due  to  cylinder 
condensation. 


SEC.  297]       CONDENSING  AND  NON-CONDENSING 


289 


297.  The  Chief  Advantages  And  Disadvantages  Of  Con- 
densing Operation  are  as  follows: 


CONDENSING 

NON-CONDENSING 

Advantages 

Disadvantages 

Decreases    steam    consumption    of 
large  engines  20  to  40  per  cent. 
Recovers  most   of  the  feed  water 
unless  a  jet  condenser  is  used  with 
impure  water.     The  recovered  feed 
water   is  usually    50    deg.  fahr. 
hotter  than  fresh  feed. 
Increases  power  output  of  a  given 
installation  or  decreases  necessary 
size  of  installation  for  given  power 
output. 
Converts  heat,  which  would  other- 
wise be  wasted,  into  work. 

Requires  more  steam. 

Must  use  fresh  feed  water  which 
may   be   expensive   to   heat   and 
purify. 

Requires  larger  boiler  installation. 

Wastes  most  of  the  exhaust  steam 
unless  it  can  be  used  for  heating. 

Disadvantages                                          Advantages 

Requires  additional  equipment,  *  i.e., 
condensing,    pumping    and    water 
recooling  equipment. 
Operation  more  difficult. 
No  steam  available  for  heating. 

Difficulty  in  keeping  j  oints  tight  and 
maintaining  additional  equipment. 

Relatively  low  first  cost. 

Operation  relatively  simple. 
Exhaust  steam  available  for  heat- 
ing. 
Fewer  joints  to  keep  tight. 

*  In  condensing  plants  these  auxiliaries  are  often  steam  driven  and 
their  exhaust  steam  is  used  to  heat  the  feed  water.  This  arrangement 
lessens  the  disadvantages  of  the  extra  equipment. 


298.  The  Most  Profitable  Degree  Of  Vacuum  Is  Greater 
With  A  Uniflow  Engine  Than  With  Simple  Or  Compound 
Counterflow  Engines. — The  most  profitable  degree  of  vacuum 
for  uniflow  engines  is  the  highest  vacuum  that  may  be  reason- 
ably maintained.  The  most  profitable  degree  of  vacuum  for 
compound  counterflow  engines  is  about  26.5  in.  of  mercury 
(or  about  88  per  cent,  of  a  complete  vacuum).  Further 

19 


290    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE     [Div.  9 

decrease  in  back  pressure  is  not  warranted  for  these  reasons: 
(1)  The  power  required  by  the  condenser  pumps  would  rapidly 
increase.  (2)  Economy  would  not  materially  increase.  (3) 
Leaks  become  troublesome.  (4)  Cylinder  condensation  is  very 
great. 

NOTE. — The  subjects  of  starting,  stopping  and.  maintaining  condensers 
are  treated  in  Div.  13. 

299.  The  Chief  Application  Of  The  Condensing  Engine  Is 
For  Electric  Power  Plants  Which  Have  A  Limited  Supply  Of 
Water,  And  For  Driving  Slow-Moving  Machinery  Which 
Cannot  Be  Turbine  Driven. — Large  modern  power  plants  are, 
whenever  possible,  located  on  a  lake  or  river  or  arm  of  the 
ocean  so  that  there  is  an  abundant  supply  of  cooling  water. 
Such  plants  nearly  always  employ  turbines,  which  operate 
with  a  higher  vacuum  than  is  profitable  with  engines,  and 
better  economies  are  thus  obtained  than  with  condensing 
engines.  Smaller  plants  which  are  not  so  located  may  employ 
condensing  engines  and  re-cool  the  condensing  water  in  a 
cooling  tower  or  pond.  Since  the  principal  use  of  the  turbine 
is  for  driving  machinery  which  permits  of  high  rotative  speeds 
(for  example,  generators  and  centrifugal  pumps),  its  applica- 
tion would  not  be  suited  to  mills  and  other  plants  where 
direct,  belt  or  rope  driving  is  employed.  In  such  plants  the 
condensing  engine  is  commonly  used  for  steam  power  genera- 
tion even  though  the  supply  of  water  is  adequate  for  econom- 
ical condensing  turbine  operation. 

QUESTIONS  ON  DIVISION  9 

1.  What  is  meant  by  condensing  operation?     How  is  it  accomplished? 

2.  Explain  by  a  diagram  how  more  power  is  developed  from  the  same  amount  of  steam 
by  condensing  operation. 

3.  What  saving  is  effected  by  condensing  operation  of  large  compound  engines? 
What  is  the  proportion  of  the  steam  required  by  the  main  engine  to  that  used  by  the 
condenser  auxiliaries? 

4.  When  is  the  condensing  operation  of  any  engine  less  economical  than  non-con- 
densing operation? 

5.  How  does  cylinder  condensation  affect  the  economies  of  engines  of  various  kinds 
when  operated  condensing? 

6.  Enumerate  the  chief  advantages  and  disadvantages  of  condensing  operation. 

7.  What  percentage  of  a  total  vacuum  is  ordinarily  profitable  in  a  condenser  for  a 
compound  engine? 

8.  Give  two  conditions  under  which  condensing  engines  are  commonly  used. 


DIVISION  10 

STEAM-ENGINE     EFFICIENCIES     AND     HOW      TO 
INCREASE  THEM 

300.  The  Steam  Engine  Converts  Into  Mechanical  Work 
Only  A 'Relatively  Small  Part  Of  The  Total  Heat  Supplied 
To  It;  see  Sec.  6.  Under  some  conditions,  the  heat  which 
is  not  converted  into  work  may  be  usefully  employed.  Under 
such  conditions  as  will  be  explained  later,  the  fact  that  the 
engine  converts  into  mechanical  work  only  a  small  part  of  the 
heat  energy  which  it  receives  becomes  of  comparatively  little 
consequence.  Under  other  conditions,  it  is  of  great  commer- 
cial importance.  For  example,  the  steam  locomotive  seldom 
converts  into  mechanical  work  over  10  per  cent,  of  the  total 
heat  supplied  to  it.  The  remaining  90  per  cent,  or  more 
produces  no  useful  effects  in  the  locomotive  and  represents 
a  total  loss.  Why  a  large  part  of  such  loss  is  unavoidable, 
and  how  the  avoidable  parts  of  it  may  be  reduced,  constitute 
the  subject  of  this  division.  See  also  the  portions  of  Div. 
12  which  relate  to  efficiency. 

NOTE. — THERE  Is  No  POSSIBLE  WAY  IN  WHICH  THE  EFFICIENCY  OF 
AN  ENGINE,  WHICH  Is  ALREADY  INSTALLED  UNDER  GIVEN  OPERATING 
CONDITIONS  AND  WHICH  Is  IN  GOOD  REPAIR,  CAN  BE  GREATLY 
INCREASED.  If  the  valves  and  pistons  of  an  engine  have  only  a  negligible 
leakage  (Div.  13)  and  the  engine  is  properly  adjusted  (Divs.  4  and  5), 
cleaned,  lagged,  and  lubricated  (Div.  16)  the  operator  has  ordinarily  no 
further  responsibility  for  its  efficiency.  It  is  sometimes  possible,  where 
the  design  of  the  engine  permits,  to  change  to  condensing  operation, 
to  superheated  steam,  or  to  higher  boiler  pressure,  in  order  to  increase 
engine  efficiency.  However,  these  operating  conditions  are  usually  so 
determined  in  a  plant  that  they  cannot  be  changed  without  completely 
rebuilding  the  plant.  When  an  engine  is  first  selected  it  should,  therefore, 
be  so  chosen  that  it  will  give  the  desired  efficiency  without  its  being 
necessary  later  to  alter  other  plant  equipment.  Therefore,  the  efficiency 
of  an  engine,  assuming  good  maintenance  and  correct  application, 
depends  entirely  on  its  design.  In  general,  the  efficiency  of  an  existing 

291 


292    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Drv.  10 

steam-power  plant  can  be  improved  by  giving  detail  attention  to  the 
boiler  room  rather  than  to  the  engine  room.  It  is  in  the  boiler  room  that 
a  great  part  of  the  correctable  wastes  occur. 

301.  Why  A  Large  Part  Of  The  Losses  In  A  Steam  Engine 
Are  Unavoidable  may  be  understood  by  a  study  of  the  hydrau- 
lic analogy  of  Fig.  355.  Fall  in  temperature,  representing  as 
it  does  loss  of  heat  or  loss  of  energy,  is  compared  to  fall  of 
water,  which  represents  loss  of  head  or  of  its  potential  energy  of 
position.  The  steam  engine,  A,  can  operate  non-condensing 
over  only  a  certain  temperature  range,  just  as  a  water-power 


er   ^ure_   _          _  J/aterAnbp_Of  Cliffy 


Fait  Of  Water 
Compared  With 


Fa//  In  Tempera  ture 


To  Datum  Plane  •£ 
evel. 


I- Engine  I- Water  Power 

FIG.  355. — Showing  analogy  between  water-power  utilized  and  heat  utilized  by  steam 

engine. 

plant  can  utilize  only  the  hydraulic  head  of  the  water  fall, 
B.  By  adding  the  condenser,  C,  an  additional  range  in 
temperature  may  be  utilized  just  as  the  fall  in  the  rapids,  D, 
might  be  utilized  by  the  water-power  plant  by  means  of 
additional  piping.  But  it  is  just  as  impractical  to  cool  to 
32  deg.  fahr.  in  the  condenser  as  it  is,  ordinarily,  to  pipe 
water  to  sea  level  to  utilize  the  final  drop  or  head  to  that 
datum  plane. 

EXPLANATION. — At  32  deg.  fahr.  water  is,  for  steam  engineering  pur- 
poses, considered  to  contain  no  heat  just  as  water  at  sea  level  is  con- 
sidered to  have  no  potential  energy.  There  is  a  large  theoretical  tem- 
perature range  to  absolute  zero  (  —  460  deg.  fahr.)  just  as  there  is  a  large 
theoretical  hydraulic  drop  from  sea  level  to  the  center  of  the  earth.  But, 


SEC.  302]  STEAM-ENGINE  EFFICIENCIES  '  293 

to  use  the  temperature  range  below  32  deg.  fahr.,  mechanical  refrigera- 
tion must  be  employed;  and  to  use  water  power  below  sea  level,  the  water 
must  be  pumped  back  to  its  original  level.  In  either  case,  no  additional 
power  would  be  developed.  It  follows  that,  although  only  a  small  part 
of  the  total  absolute  temperature  range  (and  therefore  of  the  total  heat) 
is  useful  in  the  steam  engine,  the  remainder  is  of  such  nature  that  little 
of  it  can  be  utilized. 


302.  It  Is  Often  Unwise  To  Increase  Engine  Economy  At 
The  Expense  Of  Greater  Fixed  Or  Maintenance  Charges. 

Fixed  charges  are  taxes,  insurance,  the  interest  on  the  capital 
invested  and  depreciation  or  the  amount  of  money  which  must 
be  laid  aside  yearly  to  replace  the  engine  when  it  is  no  longer 
useful  (see  Div.  15).  Steam-engine  operation  is,  ordinarily, 
a  commercial  undertaking — increased  fixed  or  maintenance 
charges  may  increase  total  power  plant  expense  as  much  as 
do  increased  fuel  costs  due  to  poor  engine  .efficiency.  There- 
fore engines  are  not,  necessarily,  built  or  operated  with  a 
view  to  securing  the  greatest  possible  thermal  efficiency. 
Instead,  they  should  be  built  and  operated  to  provide  the 
maximum  economy,  when  all  factors  of  cost  are  considered. 
Thus,  while  higher  initial  steam  temperatures  used  with  larger 
ratios  of  expansion  and  higher  vacua  increase  thermal 
efficiency,  such  methods  of  increasing  economy  are  limited 
by  the  other  costs  involved.  In  general  (see  Div.  15),  the 
fixed  charges  on  an  engine  should  be  much  less  than  the  cost 
of  the  fuel ;  and  the  engine  maintenance  charges  should  be  a 
small  fraction  of  the  total  expense  of  the  engine  during  its 
life. 

303.  The  Losses  In  A  Steam  Engine  May  Be  Divided  Into 
Three  Classes  (see  Div.  1) :  (1)  Rejection  losses  or  heat  which 
it  is  not  possible  for  a  commercial  steam  engine  to  use.     Since 
these  rejection  losses  are  largely  dependent  on  the  kind  of  cycle 
on  which  the  engine  operates,  their  amount  will  be  considered 
quantitatively  in  Sees.  314  to  316  under  the  Rankine  cycle. 
The  rejection  "  losses  "  are  often  not  lost  at  all.     All  of  the  heat 
thus  rejected  is  present  in  the  exhaust  steam  and  may  fre- 
quently be  used  for  steam  heating.     (2)  Thermal  losses  (Sec. 
309).     These   losses  nearly  always   constitute   actual  losses 
because  the  heat  thus  lost  is  too  widely  diffused  to  be  useful. 


294 


ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  10 


(3)  Mechanical  losses  (Sec.  310).  These  losses  subtract  from 
the  mechanical  work  which  has  been  derived  from  the  heat; 
and  convert  part  of  the  work  back  into  heat  in  the  bearings 
where  it  is  useless  and  particularly  undesirable. 

NOTE. — IN  A  STEAM  ENGINE,  THE  PERCENTAGE  LOSSES  ARE  A  MINI- 
MUM AT  OR  NEAR  RATED  FULL  LOAD  (Fig.  356).     At  a  considerable 


Steam  Consumption 
Lb.  Per  I.  H.  R  Hr. 

•""•>  lx>  lO  O- 

4s  <r»  a>  c 

/ 

\ 

/ 

\ 

/ 

\ 

/ 

\ 

/ 

r 

s  — 

^ 

0  50  100          150        200 

Percentage  Of  Rated  Load 

I-  Non-  Condensing 


b.  Of  Steam  Per  I.H.RHr. 

OJ  is  U1  <T 

/ 

/ 

\ 

/ 

^•x, 

* 

*s 

50  100          150         200 

Percentage  Of  Rated  Load 

n-Gondensing 


FIG.  356. — Variation  in  steam  consumption  of  uniflow  engine  with  variation  in  load. 
(Nordberg  engine,  saturated  steam.) 

overload,  the  rejection  losses  are  large  due  to  the  incomplete  expansion. 
At  light  loads,  the  mechanical  and  thermal  losses,  which  do  not  vary 
greatly  with  change  in  load,  become  larger  in  proportion  to  the  power 
output.  As  engines  are  usually  designed  to  secure  the  greatest  efficiency 
at  or  near  full  load,  it  follows  that,  in  actual  practice,  one  of  the  principal 
methods  of  maintaining  engine  efficiency  at  a  maximum  is  to  keep  the 

load  as  near  normal  (rated  full 
48  u  load)  as  is  possible.  It  also  fol- 
lows that  in  power  plants  the 
units  should  be  so  selected  that 
they  may  be  operated  at  or 
near  full  load  most  of  the  time 
(see  Div.  15). 

304.  The  Six  Principal 
Methods  Of  Decreasing 
The  Percentage  Rejection 
Losses  Of  A  Steam  Engine 

are:    (1)  Increasing    boiler 
357,  see  note  below).     (2)    Superheating  the 
(3)  Condensing  (see  Div.  9). 


l"      5.5 

75  60   85    90    95    100   105    110    115   170 
Initial  Steam  Pressure,  Lb. Per  Sq.In.  Gage 

FIG.  357. — Graph  showing  the  effect  of  in- 
creasing boiler  pressure  on  the  efficiency  of  a 
small  high-speed  non-condensing  engine. 


pressure    (Fig. 

steam  (Fig.  358,  see  Div.  14). 
(4)  Compounding  (see  Div.  8)  or  improving  the  steam  flow 
by  four-valve  and  uniflow  features  (see  Div.  11).  (5)  Vary- 
ing rotative  speed.  Relatively  slow  speed  is  an  inherent 
limitation  of  steam  engines;  hence  the  speed  cannot,  usually, 


SEC.  304] 


STEAM-ENGINE  EFFICIENCIES 


295 


be  greatly  increased.  The  most  efficient  speed  for  an 
engine  is  ordinarily  near  its  rated  speed.  The  practical 
speed  limit  for  steam  engines  (except  very  small  ones)  is 
about  300  r.p.m.  Higher  speed 
decreases  cylinder  condensation 
but  increases  wire-drawing  in 
the  valves  and  steam  ports.  To 
avoid  this  latter  effect,  the 
valves  of  higher-speed  engines 
are  made  larger.  (6)  Decreas- 
ing clearance  and  increasing  20  AO  eo  &o  100 

,  •  /.  /Ci  orvr\  Per  Cent  Of  Rated  Load 

ratio   of  expansion   (Sec.  305). 

,    ~  .  FIG.  358. — Graph   showing   the  effect 

TOO  Small   Clearance  is   danger-     of   superheating   on   the   efficiency   of.  a 

ous  since  with  small  clearance,    simple  engine- 
a  very  little  water  in  the  end  of  the  cylinder  might  cause  the 
cylinder  head  to  be  blown  out  or  the  piston  or  rod  to  be 
crushed.     Increasing  the  ratio  of  expansion  so  decreases  the 
power  output  of  an  engine  that  the  practical  limit  for  this 


Admission 
Valve-. 


FIG.  359. — Jacketed  steam-engine  cylinder.     (Rice  and  Sargent  Corliss  engine,  Provi- 
dence Engineering  Corporation.) 

ratio  is,  at  full  load,  about  8:1  for  simple  engines  and  about 
20:1  for  compound  engines. 

NOTE. — THE  PRACTICAL  LIMITS  OF  BOILER  PRESSURE  IN  STATIONARY 
POWER  PLANTS  are  about  125  Ib.  per  sq.  in.  for  simple  engines,  200  Ib. 
per.  sq  in.  for  compound  and  uniflow  engines  and  250  Ib.  per  sq.  in.  for 
triple-expansion  engines  (see  also  Sec.  428).  These  limits  are  fixed  by 
the  engine — not  by  the  boiler.  Boilers  for  turbine  service  are  being 


296    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Drv.  10 


operated  at  350  Ib.  per  sq.  in.  The  limits  are  fixed  by  the  ability  of 
engines  of  the  different  types  to  use  large  pressure  ranges  without  exces- 
sive cylinder  condensation  (see  Sec.  274).  There  is  little  advantage  in 
an  increased  boiler  pressure  unless  the  engine  can  expand  the  high-pres- 
sure steam  satisfactorily  to  nearly  the  exhaust  pressure. 

NOTE. — OTHER  POSSIBLE  METHODS  OF  DECREASING  REJECTION 
LOSSES  are:  (1)  Steam  jacketing  the  cylinders  and  receivers,  and  (2) 
using  other  working  substances  besides  steam.  (3)  Decreasing  valve  and 
piston  leakage.  Steam  jackets  (Fig.  359)  are  often  employed  as  an 
operating  convenience  to  improve  the  quality  of  the  exhaust  steam. 
The  total  losses,  because  of  the  heat  used  in  the  jacket,  are  often  greater 
with  than  without  the  jacket.  The  utilization  of  other  fluids  in  the 
same  way  steam  is  used  is  not  commercially  employed  at  present.  Some 
experiments  in  which  the  exhaust  has  been  condensed  by  a  more  volatile 
liquid  which  was  thereby  volatilized  have  proved  successful  in  decreasing 
the  rejection  losses.  Valve  and  piston  leakage  in  steam  engines  often 
causes  rejection  losses  of  10  to  20  per  cent,  even  though  the  operation 
of  the  engines  is  apparently  normal. 


305.  Clearance  Volume  Affects  The  Output  And  Economy 

Of  An  Engine. — It  is  necessary 
for  good  operation  of  high- 
speed engines  to  compress  the 
steam  in  the  clearance  volume 
almost  to  the  throttle  pressure. 
In  low-speed  engines,  the  most 
economical  compression  may 
be  one-third  or  less  of  the 
throttle  pressure.  Due  to  the 
area  under  the  compression 
line — that  is,  the  work  done 
in  compressing  the  steam — 
the  output  and  efficiency  of  an 
engine  will  ordinarily  be  less 
with  larger  clearance  volume. 


.Compression  With 
;  Large  Clearance 

IM 

-  Expansion  W/th 

Q ->i  ~ 

%ti     I-W«al    . 

§  expansion        -^\,x 

J^.g  N^^agraHBm^^rk 

N  \       <^%^^ompre55bnWith5mall\\{ 
V^.vJ     M^^%^y?>^  ,-CLearance 
I__L_     "       ~ 


FIG.  360. — Showing  how  less  power  is 
derived  from  the  same  amount  of  steam 
when  the  clearance  volume  is  larger. 


EXPLANATION. — Fig.  360-1  shows  two  superimposed  ideal  indicator 
diagrams  having  expansion  lines,  MN  and  MNi.  The  solid-line  diagram 
has  a  clearance  volume,  Cj,  of  3  per  cent.  Compression  occurs  at  A 
and  t.hg_p.uahinn  stftam  is  compressed  along  line  R,  to  about  one-half 
throttle  pressure.  The  dashed-line  diagram  has  a  clearance  volume,  C2, 
of  15  per  cent.  Compression  then  occurs  at  B  and  the  cushion  steam  is 
compressed  along  line  S.  The  shaded  area  between  lines,  R  and  S, 
then  represents  the  loss  in  work  due  to  the  larger  clearance  volume,  C2. 


SEC.  306] 


STEAM-ENGINE  EFFICIENCIES 


297 


The  steam  is  compressed  to  the  same  theoretical  point,  D,  on  the  throttle 
pressure  line  so  that  the  amount  of  steam  used,  Q,  is  the  same  in  both 
diagrams.  With  the  larger  clearance,  there  is  a  slight  gain  in  work  on 
the  expansion  line  represented  by  the  shaded  area,  MNN\.  This  area 
would  be  equal  to  the  area  RS,  if  the  expansion  were  carried  out  to  back 
pressure  but,  with  incomplete  expansion,  area  MNNi  is  smaller  than 
area  RS.  Fig.  360-11  shows  the  difference  between  the  clearance  losses 
in  actual  Corliss  and  automatic-engine  diagrams.  The  wire-drawing  at 
W  in  the  automatic-engine  diagram  nullifies  the  theoretical  gain  due  to 
larger  clearance  shown  at  N\  in  I. 

306.  Table  Showing  Typical  Values  For  Clearance  In 
Engines  Of  Different  Types,  based  partly  on  data  from  Marks' 
MECHANICAL  ENGINEERS'  HANDBOOK  : 


Engine 


Clearance   as   a   percentage   of 
the  displacement  volume 


High  value 


Low  value 


Flat  slide  valve  at  side  of  cylinder 

Piston  valve  at  side  of  cylinder 

Corliss  valves 

Poppet  valves 


10 
15 

8 
4 


5 
7 
2 
1.5 


307.  Cylinder  Condensation  Is  The  Cause  Of  Part  Of  The 
Rejection  And  Thermal  Losses  in  a  steam  engine.     The  three 
causes  of  cylinder  condensation  are:  (1)  The  natural  mixing 
of  the  supplied  steam  with  the  colder  steam  in  the  clearance 
space.     This  can  be  greatly  reduced  by  using  high  compres- 
sion pressures.     (2)  Alternate  exposure  of  the  cylinder  walls  to 
the  live  steam  and  exhaust  steam.     Condensation  due  to  this 
cause   is   partly  avoided   by   compounding  and   use   of  the 
uniflow  principle.     (3)  Radiation  of  heat  through  the  cylinder 
walls.     This  is  considered  a  thermal  loss  (Sec.  309). 

NOTE. — JACKETING  (Fig.  359)  PREVENTS  SUCH  CONDENSATION  IN 
THE  CYLINDER  PROPER  As  Is  DUE  To  RADIATION.  However,  condensa- 
tion takes  place  in  the  jacket,  and  often  exceeds,  in  amount,  the  saving 
due  to  no  condensation  in  the  cylinder  proper.  Jackets  are  useful  in 
keeping  cylinders  warm  or  warming  them  up  in  starting. 

308.  Where  The  Exhaust  Steam  Can  Be  Economically  Used 
For  Heating,  the  rejection  losses  are  of  little  consequence. 


298     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  10 

Many  power  plants  which  furnish  both  power  and  heat  use 
large,  simple  slide-valve  engines  and  make  few  provisions  for 
reducing  rejection  losses.  The  power  plant  may  then  be 
50  to  80  per  cent,  efficient  because  the  exhaust  steam  is  used 
for  heating.  The  plant  then  has  no  rejection  losses — only 
mechanical  and  thermal  losses.  The  performance  of  the 
engine  itself  is  no  better  under  these  conditions  than  if  the 
rejected  heat  were  lost  but  the  expense  of  the  rejected  heat 
cannot,  when  the  exhaust  is  used,  be  charged  to  the  engine  as  it 
can  when  the  live  steam  is  used,  for  power  only. 


Losses  In  The       ,.p 
Piping  1. 4  %'•>• 


Losses  In  Piping  1.1%' 
•Loss  By  Cooling  Of 
Conctensate  1.1% 


FIG.  361. — Showing  heat  balance  in  a  power  plant  in  which  the  engine  exhaust  is  used  for 

heating. 


EXPLANATION. — The  advantage  of  using  an  engine's  exhaust  steam  for 
heating  where  both  power  and  heat  are  desired  may  be  understood  by 
comparing  Fig.  361  with  Fig.  362.  In  Fig.  361,  it  is  shown  that,  with  the 
exception  of  boiler  losses  and  small  piping  losses,  PI,  nearly  all  of  the 
heat,  HI,  imparted  to  the  steam  in  the  boiler  appears  either  as  work  or  as 
useful  heat.  In  Fig.  362,  part  of  the  steam,  G2,  is  used  directly  for  heating 
and  the  rest,.  Ez,  for  operating  a  condensing  engine.  There  is  then  a 
large  heat  loss  in  the  condenser.  Less  power  is  developed  by  the  Fig. 
362  arrangement  and  less  heat  is  available  from  the  same  original  supply 
than  is  available  with  the  arrangement  shown  in  Fig.  361.  Thus  it  is 
evident  that  although  the  efficiency  of  an  engine  may  be  low,  the  efficiency 


SEC.  309] 


STEAM-ENGINE  EFFICIENCIES 


299 


of  the  combined  power  and  heating  plant  in  which  the  engine  is  used 
may  be  very  high. 


Heat  Transformed  Into  Work  5.9% 


'Losses  By        ''Heat  Carried 
Cooling  Of        Away  By 
Drain  Water      Water  Of 
0.7%  Condensation 

30.2% 


FIG.  362. — Heat  balance  in  a  plant  operating  a  condensing  engine  and  using  live  steam 

for  heating. 

309.  The  Principal  Method  Of  Reducing  Thermal  Losses 

is  by  employing  heat  insulation  or  lagging  on  the  cylinder 


.-Throttle-Valve 
Body 

.'Steam 
Valve 


Exhaust  Valves 
FIG.  363.— Well  heat- insulated  engine  cylinder.      (Cooper  Corliss  engine.) 

walls.     The  heat  conductivity  of  the  metal  parts  of  an  engine 
cylinder  is  fairly  high  and,  therefore,  if  they  are  exposed  to 


300     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  10 

the  steam  on  one  side  and  the  air  on  the  other,  they  conduct 
much  heat  from  the  steam  to  the  air.  A  layer  of  porous  non- 
metalic  material  such  as  magnesite,  asbestos,  or  diatomaceous 
earth  (L,  Fig.  363)  is  packed  around  the  cylinder  walls  to 
reduce  radiation.  The  transmission  of  steam  from  one 
point  to  another  always  involves  a  thermal  loss.  The  fact 
that  transmitting  any  form  of  energy  involves  a  loss  is  illus- 
trated by  the  losses  in  the  electric  circuits  of  Fig.  364. 


6.5% 


Boiler  &  Chimney  Loss   zau/fei • 

Pipe  Loss I: I, 

Rejected  In  Exhaust i- 

Loss  In  Engine  Cylinder---- 


58.7% 


Loss  In  Engine  And  Generator 
Line  And  Transformer  Loss 


Delivered  To  Lamps  Or  Motors  .........  7.70%  '- 


Sub-Station         Street    Railway  a6°/°' 
1.70% 


FIG.  364. — Showing  energy  balance  (losses  and  useful  energy)  in  typical  electric- 
energy  distribution  circuits  based  on  a  chart  from  Power.  (The  heavy  figures  represent 
energy  lost  or  used  in  British  thermal  units  per  pound  of  coal  fed  to  the  furnace  based 
on  a  coal  which  has  a  heating  value  of  13,543  B.t.u.  per  pound.  The  lighter  figures 
indicate  percentages  of  the  total  heat.  The  calculations  were  made  on  the  basis  that 
the  generator  is  supplying  power  to  only  one  of  the  three  circuits — either  the  machine 
shop,  the  street  railway,  or  the  street  lamps.  Should  more  than  one  circuit  be  in  use  at 
any  time,  the  energy  available  for  these  circuits  would  still  total  9.4  per  cent.,  as  shown 
below  the  dashed  dividing  line  in  the  list,  but  it  would  be  divided  among  the  circuits  in 
use.  The  diagram  does  not  show  the  losses  which  are  listed  above  the  dashed  dividing 
line  of  the  list.) 

310.  The  Two  Principal  Methods  Of  Reducing  Mechanical 
Losses  In  An  Engine  are:  (1)  Designing  the  engine  so  as  to 
minimize  pressures  on  bearing  surfaces.  (2)  Proper  lubrica- 
tion (see  Div.  16).  Large  bearings  using  thick  oil  have  more 
friction  than  do  smaller  bearings  using  thinner  oil.  But, 
for  satisfactory  operation,  the  bearing  area  and  viscosity 
of  the  oil  must  be  such  that  an  oil  film  will  always  be  main- 


SEC.  311] 


STEAM-ENGINE  EFFICIENCIES 


301 


tained  between  the  rubbing  surfaces.  A  vertical  engine  has 
slightly  less  friction  than  a  similar  horizontal  one.  Because 
of  their  vertical  position,  the  rapidly  moving  parts — that  is, 
the  piston  and  crosshead — have  little  tendency  to  press 
against  the  cylinder  and  guides.  An  engine  running  "under" 
(Sec.  32)  has  less  friction  on  the  guides  than  one  running 
"over"  because  when  running  under  the  thrust  of  the  connect- 
ing rod  partially  supports  the  crosshead.  Stationary  engines 
are  commonly  built  horizontally  (Sec.  25)  (because  of  the 
simpler  balancing  and  framework)  and  run  "over,"  in  spite 


15        50       15 


5rake    Horse    Power 


FIG.  365. — Showing  variation  in  friction  horse  power  with  variation  in  brake  horse 

power  developed. 

of  the  differences  in  friction,  as  a  rule  (because  of  the  easier 
maintenance) ;  see  Div.  13.  The  frictional  losses  of  all  engines 
increase  somewhat  with  the  power  which  the  engine  develops 
as  indicated  in  Fig.  365  which  is  taken  from  Gebhardt's  STEAM 
POWER  PLANT  ENGINEERING. 

311.  Engine  Friction  Comprises  Principally:  (1)  Bearing 
friction.  (2)  Valve  friction.  (3)  Gland  friction.  Bearing 
friction  is  reduced  to  a  minimum  by  the  use  of  low-friction 
combinations  of  metals.  Thus,  hard  steel  running  in  babbitt 
metal  for  main  bearings  (Fig.  366)  and  hard  steel  on  bronze 
bushings  for  connecting-rod  bearings  (Fig.  367)  are  widely 
used.  Piston  friction  may  be  reduced  by  means  of  low-friction 
metal  inserts  (Fig.  368)  in  the  wearing  face  of  the  piston. 
Friction  in  slide  and  poppet-valves  is  reduced  by  balancing 
the  valves  (see  Divs.  4  and  5).  Gland  friction  may  be  re- 


302    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  10 


duced  by  using  metallic-faced  packing  (Fig.  369)  and  other 
low-friction  packings — being  careful  never  to  have  the  packing 
pressed  too  tightly  against  its  rod. 


Vertical 


Wedge  For 


Oil-Cup  Hole-. 


Cast  Iron  Bearing  Quarter 


FIG.  366. — Showing  low-friction — bab- 
bitt— metal  inserted  in  main  bearing. 
(Erie  Ball  Engine  Co.) 


Ring 
Section- 


FIG.  367.  —  Bronze-bushed    connecting- 
rod  bearing.     Closed-end  type. 


Low- Friction  Metal  Rings  - . 


I-Detail  Of  Rin0 


H-Half  Cross-Section  I-Section  Along  A.C.B 


FIG.  368. — Piston  designed  to  reduce  friction  and  wear  by  means  of  low-friction  bull- 
rings, GG.  (The  single  expansive  ring  E  is  used  to  make  a  tight  contact  with 
the  cylinder  walls.) 

312.  Mathematical  Methods  Of  Computing  Steam-Engine 
Efficiencies  will  be  discussed  in  the  remainder  of  this  division. 
The  preceding  sections  considered,  in  a  general  way,  the 
causes  of  steam-engine  losses  and  the  common  methods  of 
minimizing  them.  To  calculate  the  exact  effect  of  changes 


SEC.  313] 


STEAM-ENGINE  EFFICIENCIES 


303 


^Sectional  Metallic  Packing  Ring 
•Forced  Or  Gravity  Oil  Feed 

Ring 
\  Gasket 


in  operating  conditions  which  were   previously   mentioned, 
the  mathematical  methods  which  herein  follow  may  be  em- 
ployed.    Before  proceeding  consult  the  portions  of  Div.   1 
which  discuss  the  relations  be- 
tween heat  and  work  and  energy 
and  also  those  portions  of  Div. 
12  which  relate  to  efficiency. 

313.  Various  Ways  In  Which 
The  Efficiency  Of  A  Steam 
Engine  Is  Commonly  Expressed 
are  as  follows:  (1)  Based  on 
indicated  horse  power,  it  may  be 
expressed  as:  (a)  Thermal  effi- 
ciency based  on  indicated  horse 
power,  Edti  in  Fig.  370.  (6) 
Pounds  of  steam  used  per  indi- 
cated horse  power  hour,  (c) 
Pounds  of  coal  burned  per  indi- 
cated horse  power  hour,  (d) 
British  thermal  units  per  indicated  horse  power  minute,  (e) 
Thermal  efficiency  based  on  indicated  horse  power  compared  to 
the  ideal  Rankine  cycle,  also  called  cylinder  efficiency. 


'*          '  Vanadium  Cas  t  Iron 
'Springs  Hold  Rings  To  Shaft 

FIG.  369. — Piston-rod  gland  packing 
having  low-friction  metal  wearing  face. 
(Erie  City  Iron  Works.) 


^Efficiency  Of  The  Rankine  Cycle 

Ideal  Rankine  Cycle  Ratio 

Ratio  Gives 


Mechanical 
Efficiency 


,::  Thermal  Efficiency 

Ratio  Gives 
~~ 


Edtb=0ver-AU  Efficiency 
FIG.  370. — Chart  showing  relation  between  the  various  engine  efficiency  standards. 

(2)  Based  on  brake  horse  power,  it  may  be  expressed  as: 
(a)  Over-all  thermal  efficiency  or  efficiency  based  on  brake 
horse  power,  Eda>  in  Fig.  370.  (b)  Pounds  of  steam  per 


304     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  10 

brake  horse  power  hour,  (c)  Pounds  of  coal  per  brake  horse 
hour,  (d)  British  thermal  units  per  brake  horse  power  hour, 
(e)  British  thermal  units  per  kilowatt  hour.  (/)  Pounds  of  coal 
per  kilowatt  hour. 

(3)  Mechanical  efficiency,  Edm  in  Fig.  370. 

NOTE. — THE  STEAM  CONSUMPTION  is  ordinarily  calculated  for  the 
engine  on  a  dry-steam  basis.  Engine  manufacturer's  performance  speci- 
fications are  practically  always  computed  on  this  basis.  The  weight  of 
dry  steam  is  the  weight  of  the  wet  steam  multiplied  by  its  quality, 
expressed  decimally.  A  little  water  suspended  in  the  steam  does  not 
decrease  the  engine  efficiency  when  the  efficiency  is  computed  on  a  dry- 
steam  basis  (See  the  A.S.M.E.  TEST  CODE  in  Sec.  381).  But  the  water, 
of  course,  does  no  work.  Hence,  when  an  accurate  determination  is 
being  made,  the  presence  of  the  water  must  be  considered  and  the 
apparent  efficiency  decreased  accordingly.  In  any  case,  the  efficiency 
is  proportional  to  the  quality  of  the  steam. 

NOTE. — THE  "THEORETICAL  EFFICIENCY"  DEFINED  IN  Div.  1  is 
very  nearly  equal  to  the  thermal  efficiency  as  shown  in  Fig.  370.  The 
"theoretical  efficiency"  in  Div.  1  includes  a  small  amount  of  losses  by 
radiation  from  the  engine  whereas  the  thermal  efficiency  includes  only 
the  net  indicated  work.  The  "theoretical  efficiency"  is  not  ordinarily 
computed  in  power  plant  testing. 

314.  The  Ideal  Rankine  Cycle  Is  Frequently  Used  In 
Steam-Engine  Testing  As  A  Standard  Of  Engine  Performance. 

(See  note  below  and  also  the  author's  PRACTICAL  HEAT.) 
The  ideal  Rankine  cycle  (Sec.  8;  also  called  the  Clausius 
cycle)  is  the  most  nearly  perfect  cycle  upon  which  a  commer- 
cial steam  engine  can  operate.  It  is,  therefore,  the  logical 
cycle  with  which  to  compare  steam-engine  performance.  A 
mechanically  perfect  engine  without  friction,  without  clear- 
ance losses,  with  perfectly  non-conducting  cylinder  walls, 
and  which  expanded  the  steam  from  exactly  throttle  pressure 
to  exactly  back  pressure,  would  develop  all  of  the  power  of  the 
ideal  cycle  (see  Fig.  7) .  Since  no  actual  engine  can  have  all  of 
these  characteristics,  no  engine  can  have  as  great  an  efficiency 
as  the  ideal  Rankine  cycle  on  which  it  operates. 

NOTE. — A  RANKINE  CYCLE  MAY  HAVE  CLEARANCE  AND  STILL  BE 
IDEAL.  That  is,  clearance  does  not  involve  a  loss,  provided  compression 
is  so  timed  that  the  steam  in  the  clearance  space  is  compressed  to  throttle 


SEC.  315] 


STEAM-ENGINE  EFFICIENCIES 


305 


pressure.     Thus  I  and  II  (Fig.  371)  show  ideal  performance  but  III, 
having  terminal  drop,  T,  is  less  efficient. 

NOTE. — AN  ENGINE  CYCLE  is  understood  to  mean  the  series  of  repeat- 
ing processes  which  occur  in  the  engine  cylinder.  The  cycle  is  con- 
veniently pictured  on  the  indicator  diagram,  which  is  thus  a  cycle 
diagram.  Thus,  in  a  practical  steam  engine  the  cycle  diagram  is  com- 
posed of  (as  shown  in  Fig.  88)  an  admission  line,  a  steam  line,  an  expansion 
line,  a  release  line,  an  exhaust  line,  and 
a  compression  line.  Moreover,  the 
exact  cycle  of  any  particular  steam 
engine  is  further  determined  by  the 
pressure  variations  along  each  of 
these  lines. 


I-Oriojinal    Ideal 
Rankine  Cycle 


315.  To  Compute  The  Effi- 
ciency Of  The  Ideal  Rankine 
Cycle  for  any  set  of  operating 
conditions,  use  the  following 
formula: 

H  ti  — 


(29)  Edt 


(a  decimal) 


•  Clearance 


H-  Ideal  Rankine 
Cycle  With 
Clearance 

Loss) 


M- Modified  Rankine 
Cycle.  Terminal 
Drop  Involves  Loss 


T 


FIG.  371.  —  Showing    two   forms   of 


Hii- 

Wherein:  Edt  =  the  thermal 
efficiency  of  the  ideal  Rankine 
cycle,  expressed  decimally.  Hti 
=  the  total  heat  per  pound  of 
steam  as  admitted  to  the  engine.  the  ideal  Rankine  cycle  and  Codified 

,  '  ,      Rankine  cycle. 

Ht2  =  the  total  heat  per  pound 

of  steam  as  exhausted  from  the  engine,  assuming  that  it 
expands  adiabatically  from  the  conditions  of  Ht\.  Hi2  =  the 
heat  of  liquid  at  the  temperature  and  pressure  at  which  the 
steam  is  exhausted. 

DERIVATION.— In  general,  thermal  efficiency  =  heat  converted  into 
work  -f-  heat  input.  The  heat  converted  into  work  in  the  ideal  Rankine 
cycle,  since  there  is  no  thermal  loss,  is  the  difference  between  the  heat 
present  in  the  steam  admitted  and  that  present  in  the  steam  exhausted — 
or  Hti  —  Htz-  The  heat  input  is  the  amount  of  heat  which  must  be 
supplied  to  the  water  at  the  exhaust  temperature  to  convert  it  to  steam 
at  the  admission  temperature  and  pressure,  namely  (Ht\  —  Hit).  Hence 
the  efficiency  =  heat  converted  into  work  -f-  the  heat  input  =  (Hti  —  Htz) 

EXAMPLES. — Compare  the  efficiencies  of  ideal  Rankine  cycles  under 
the  following  conditions:    (1)  95  per  cent,  quality  steam  at  100  Ib.  per 
20 


306    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.   10 

sq.  in.  abs.  and  20  Ib.  per  sq.  in.  abs.  back  pressure.  (2)  Saturated 
steam  at  175  Ib.  per  sq.  in.  abs.  to  1  Ib.  per  sq.  in.  back  pressure.  (3) 
Superheated  steam  at  175  Ib.  per  sq.  in.  abs.  and  200  deg.  fahr.  superheat 
to  1  Ib.  per  sq.  in.  abs.  back  pressure. 

SOLUTIONS. — Find  the  total  heats  from  a  total-heat-entropy  chart  or 
temperature-entropy  chart  such  as  that  found  in  the  author's  PRACTICAL 
HEAT  and  find  the  heats  of  liquids  from  the  steam  table.  By  For.  (29), 
the  thermal  efficiency,  Edt  =  (Hti  —  Ht<i)/(Hn  —  Hi2)  or: 

For  condition  (1),  Edt  =  (1138  --  1025)  -=-  (1138  -  196)  =  0.120 
=  12.0  per  cent. 

For  condition  (2),  Edt  =  (1197  -  809)  +  (1197  -  70)  =  0.291  =  29.1 
per  cent. 

For  condition  (3),  Edt  =  (1307  -  937)  +  (1307  -  70)  =  0.299  =  29.9 
per  cent. 


FIG.  372. — Showing  steam  and  feed-water  cycle  in  power  plant. 


NOTE. — WHY  THE  HEAT  OF  THE  LIQUID  AT  THE  TEMPERATURE  OF 
THE  EXHAUST  Is  TAKEN  As  A  BASIS  IN  CALAULATING  EFFICIENCY  may 
be  understood  by  referring  to  Fig.  372.  The  exhaus  steam  is,  or  may  be. 
condensed  and  returned  to  the  boiler  as  feed  water.  The  heat  which 
must  be  imparted  to  the  water  to  convert  it  into  steam  at  the  condition 
at  which  it  is  to  enter  the  engine  is  thus  added  by  the  boiler  to  that  already 
contained  in  the  feed  water.  Actually  the  feed  may  be  returned  at  a 
higher  or  a  lower  temperature  than  that  of  the  engine  exhaust  because  of 
the  losses  in  the  condenser,  C,  and  gains  in  the  heater,  F;  but  such  tem- 
perature differences  are  considered  to  be  due  to  the  other  power  plant 
equipment  and  not  to  the  engine  itself.  If  the  exhaust  steam  were 
merely  condensed  in  C — not  further  cooled  after  condensation — then  the 
condensate  would  have  the  same  temperature  as  has  the  exhaust  steam; 
that  is,  its  heat  content  would  be  Hit. 


SEC.  316]  STEAM-ENGINE  EFFICIENCIES  307 

316.  To  Compute  The  Theoretical  Water  Rate  Based  On 
The  Ideal  Rankine  Cycle  (also  called  the  Rankine  water  rate) 
use  the  following  formula: 

2545 

(30)  Ws  =  H     _  H  (lb.  per  h.p.  hr.) 

Wherein:  Ws  =  weight  of  steam,  in  pounds,  used  per  horse 
power  hour,  or  the  water  rate.  Hti  =  the  total  heat  of  steam 
per  pound  as  admitted  to  the  engine.  Htz  =  the  total  heat  per 
pound  of  steam  as  exhausted  from  the  engine,  assuming  that  it 
expanded  adiabatically  from  the  conditions  of  Ht\. 

DERIVATION.  —  There  are  778  ft.  lb.  in  1  B.t.u.;  also  there  are  33,000 
X  60  ft.  lb.  in  1  h.p.  hr.  Therefore,  there  are  33,000  X  60  H-  778  =  2545 
B.t.u.  in  1  h.p.  hr.  output.  But  from  each  pound  of  steam  there  are 
abstracted  by  the  expansion  (Ht\  —  Ht2)  B.t.u.  That  is,  the  heat  input 
converted  into  work  is  the  difference  between  the  heat  contents  of  the 
admitted  and  the  exhausted  steam.  Therefore,  the  number  of  pounds 
of  steam  required  for  each  horse  power  hour  =  2,545  -r-  (Ht\  —  H^). 

EXAMPLE.  —  What  is  the  theoretical  water  rate  of  an  engine  operating 
on  98  per  cent,  quality  steam  at  165  lb.  per  sq.  in.  abs.  and  exhausting 
at  212  deg.  fahr.  SOLUTION.  —  By  the  temperature-entropy  chart,  the 
total  heats  are,  respectively,  1175  and  1005  B.t.u.  By  For.  (30),  the 
water  rate,  Ws  =  2545/(#«  -  Ht2)  =  2545  -*-  (1175  -  1005)  =  15.0 
lb.  per  h.p.  hr. 

317.  To  Compute  The  "Thermal  Efficiency  Of  An  Engine 
Based  On  Indicated  Horse  Power,"  use  the  following  formula: 

2545 

(a  dedmal) 


Wherein  :  Edti  =  the  thermal  efficiency  of  an  engine,  expressed 
decimally,  based  on  indicated  horse  power.  WSi  =  the  actual 
weight  of  steam  consumed,  in  pounds  per  indicated  horse 
power  per  hour  as  shown  by  test  (Div.  12).  Hn  =  the  total 
heat  per  pound  of  the  steam  as  admitted  to  the  engine. 
Hi2  =  the  heat  of  liquid  as  found  in  a  steam  table,  at  the 
temperature  of  the  engine  exhaust. 

DERIVATION.  —  Always  the  efficiency  =  the  output  -r-  the  input.  The 
heat  equivalent  of  one  indicated  horse  power  hour  output  of  work  is 
2545  B.t.u.  The  heat  "input"  consumed  by  the  engine  in  producing 
this  2545  B.t.u.  of  work  output  is  the  weight  of  steam  used  (Wsi)  multi- 
plied by  the  heat  brought  from  the  boiler  by  each  pound  (Ht\  —  Hit) 
or:  W,i(Hti  —  Hit).  Hence  the  efficiency,  Edn  =  output  -j-  input  =» 
2545  -=-  W*(Hn  -  Hit). 


308    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  10 

NOTE. — Now  when  the  steam  admitted  is  dry  and  saturated,  its  total 
heat  may  be  found  in  a  saturated  steam  table;  when  superheated,  it  may 
be  found  in  a  superheated  steam  table.  Its  heat  for  any  condition  may 
be  found  on  a  total-heat-entropy  chart  or  a  temperature-entropy  chart 
Also,  when  wet  (as  is  usually  the  case)  the  total  heat  may  be  calculated  by 
the  following  formula: 

(32)  Hn  =  xdHv  +  Ht  (B.t.u.  per  Ib.) 

Wherein:  xd  =  the  quality  of  the  steam,  expressed  decimally.  Hv  = 
the  latent  heat  per  pound  of  steam.  HI  =  the  heat  per  pound  of  liquid 
at  the  steam  temperature.  Also  the  total  heat  of  steam  when  super- 
heated may  be  calculated  from  the  following  formula: 

(33)  Htl  =  Hd  +  TnCm  (B.t.u.  per  Ib.) 

Wherein:  Hd  =  the  total  heat  per  pound  of  dry  saturated  steam  at  the 
same  pressure.  Cm  =  the  mean  specific  heat  of  the  superheated  steam 
as  taken  from  a  mean  specific  heat  chart  such  as  that  found  in  the  author's 
PRACTICAL  HEAT.  Tn  =  the  number  of  degrees  Fahrenheit  of  superheat. 
EXAMPLE. — What  is  the  thermal  efficiency  of  an  engine  which  uses 
30  Ib.  of  95  per  cent,  quality  steam  at  100  Ib.  per  sq.  in.  abs.  The 
temperature  of  the  exhaust  is  228  deg.  fahr.  SOLUTION. — The  total 
heat  of  the  wet  steam,  Htl  =  xdHv  +  HI  =  0.95  X  888  +  298  =  1142 
B.t.u.  The  thermal  efficiency,  Edli  =  2545/W«-(#a  -  #J2)  =  2545 
-f-  30  X  (1142  -  196)  =  0.090  =  9.0  per  cent. 

318.  The  Water  Rate  Of  A  Steam  Engine  Is  Usually  Taken 
As  A  Measure  Of  Its  Economy. — Although,  as  shown  by 
For.  (30),  the  water  rate  is  not  really  a  measure  of  its  effi- 
ciency— the  efficiency  of  an  engine,  depending  also  on  the 
state  of  the  steam  supplied  to  it  and  the  pressure  at  which  it 
exhausts — the  water  rate  is  more  useful  than  the  efficiency 
when  the  economy  of  the  entire  plant  is  considered  in  conjunc- 
tion with  the  performance  of  the  engine.  This  may  be  a 
fallacy  arising  from  the  manner  in  which  plant  operation  is 
usually  computed;  but,  since  no  better  method  of  calculation 
has  yet  been  devised,  and  since  the  water  rate  method  is 
comparatively  simple,  this  method  will  be  followed  in  later 
divisions.  The  simplicity  of  the  water  rate  method  of 
computing  plant  economy  arises  from  the  facts  that:  (1)  The 
water  rate  of  an  engine,  when  operating  under  certain  steam 
pressures  and  temperatures,  is  independent  of  what  further 
use  is  made  of  the  steam  after  it  leaves  the  engine.  (2)  The 
water  rate  of  an  engine  usually  determines,  very  nearly,  the 


SEC.  319]  STEAM-ENGINE  EFFICIENCIES  .     309 

amount  of  steam  which  must  be  generated  in  the  boiler  and, 
therefore,  the  size  of  the  boiler.  (3)  The  water  rate  is  more 
directly  measureable  from  the  readings  of  instruments  (see  Div. 
12).  The  efficiency  is  usually  determined  from  the  same  readings 
but  involves  further  calculation.  (4)  The  water  rate,  when 
considered  in  combination  with  the  steam  pressures  and  tem- 
peratures, gives  an  experienced  engineer  a  good  idea  of  the 
engine's  efficiency.  However,  one  must  not  lose  sight  of  the 
fact  that  the  water  rate  alone  does  not  give  a  complete 
indication  of  efficiency. 

EXAMPLE. — Assume  that  engine  No.  1  uses  25  and  engine  No.  2,  23  Ib. 
of  steam  per  indicated  horse  power  hour.  Engine  No.  1  operates  on 
saturated  steam  at  100  Ib.  per  sq.  in.  abs.  and  exhausts  against  5  Ib.  per 
sq.  in.  gage  back  pressure.  Engine  No.  2  operates  on  saturated  steam 
at  190  Ib.  per  sq.  in.  abs.  and  exhausts  condensing  at  2  Ib.  per  sq.  in.  abs. 
Compare  their  thermal  efficiencies.  SOLUTION. — By  For.  (30)  the  thermal 
efficiency,  Edti  =  2545/Wsi  (Htl  -  H12)  =  2545  -*•  25(1186  -  196)  =  10.3 
per  cent,  for  engine  No.  1.  Edti  =  2545  +  23(1197  -  94)  =  10.0 
per  cent,  for  engine  No.  2.  Therefore  engine  No.  2,  although  it  uses  less 
steam,  has  a  lower  thermal  efficiency  than  engine  No.  1. 

319.  The   Efficiency   Of   An   Engine    Compared   To   The 
Ideal  Rankine  Cycle   (often  called  the  Rankine  cycle  ratio 
or  cylinder  efficiency)  is  the  ratio  of  its  actual  thermal  efficiency 
to  the  efficiency  of  the  ideal  Rankine  cycle  for  the  same  operat- 
ing conditions.     Or,  as  a  formula: 

(34)  Rankine  cycle  ratio  —  Actual  thermal  efficiency  -j-  Rankine 
cycle  efficiency. 

EXAMPLE. — The  efficiency  of  the  ideal  Rankine  cycle  under  conditions 
(1)  Sec.  315,  is  12  per  cent.  The  actual  thermal  efficiency  under  the 
same  conditions  (Sec.  317)  was  9  per  cent.  The  Rankine  cycle  ratio 
is  then  9.0  -r-  12.0  =  0.75. 

320.  A  Table   Showing  Typical  Values  Of  The  Rankine 
Cycle  Ratios  For  Engines  Of  Different  Types  (from  Marks' 
MECHANICAL  ENGINEERS'  HANDBOOK): 


Type  of  engine 

Condensing 

Non-condensing 

Simple  

0.4 

0.6 

Compound     ... 

0  5 

0.65 

Triple-expansion 

0  6 

310     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.   10 

321.  The  Mechanical  Efficiency  Of  An  Engine  is  the  ratio 
of  its  brake  horse  power  to  its  indicated  horse  power.     The 
two  horse  powers  are  understood  to  be  measured  simultane- 
ously (see  Div.  12). 

(35)  Edm  =  ^  (a  decimal) 

*»$ 

Wherein:  Edm  =  the  mechanical  efficiency  of  the  engine, 
expressed  decimally.  PbhP  =  the  brake  horse  power.  Pihp 
=  the  indicated  horse  power  developed  at  the  same  time 
during  which  PbhP  was  delivered.  For  other  relations 
between  indicated  and  brake  horse  powers,  see  Sec.  127. 

EXAMPLE.  —  An  engine  delivers  227  brake  horse  power  while  the  indi- 
cated horse  power  is  235.  What  is  the  mechanical  efficiency?  SOLU- 
TION. —  By  For.  (35),  the  mechanical  efficiency,  Edm  =  P^p/Pap  =  227 
-r-  235  =  0.966  =  96.6  per  cent. 

322.  The    Over-All    Efficiency    Or    "Thermal    Efficiency 
Based  On  Brake  Horse  Power"  is  computed  in  the  same  way 
as  that  based  on  indicated  horse  power  except  that  the  water 
rate  per  brake  horse  power  is  used.     Thus,  For.  (30)  becomes: 

(36)  Edtb  =      ~7  —  ~~  (a  decimal) 


Wherein:  Edtb  =  the  thermal  efficiency,  decimally  expressed, 
based  on  brake  horse  power.  Ws&  =  weight  of  steam  con- 
sumed per  brake  horse  power  hour.  Ht\  =  the  total  heat  per 
pound  of  steam  as  admitted  to  the  engine.  Hn  =  the  heat 
of  liquid  per  pound  at  the  temperature  of  the  exhaust. 

EXAMPLE.—  An  engine  uses  16  Ib.  of  steam  per  brake  horse  power  hour. 
If  the  total  heat  of  steam  as  admitted  to  the  engine  is  1190  B.t.u.  per 
Ib.,  and  the  heat  of  liquid  at  exhaust  temperature  is  90  B.t.u.  per  Ib. 
what  is  the  over-all  efficiency  of  the  engine?  SOLUTION.  —  By  For.  (36), 
the  over-all  efficiency,  Edtb  =  2545/Wi6(#u  -  Hi2)  =  2545  -r  16(1190 
-  90)  =  0.145  =  14.5  per  cent. 

323.  The  Other  Measures  Of  Engine  Efficiency  given  in 
Sec.  313  are  found  by  test  or  may  be  computed  as  follows: 
The  British  thermal  units  per  brake  or  indicated  horse  power 
hour  may  be  computed  by  multiplying  the  number  of  pounds  of 


SEC.  323]  STEAM-ENGINE  EFFICIENCIES  311 

steam  used  per  horse  power  per  hour  by  the  total  heat  of 
steam  as  admitted  minus  the  heat  of  liquid  of  the  exhausted 
steam.  Kilowatt  hour  values  may  be  found  by  applying 
the  relation  1  h.p.  =  0.746  kw.  Thus: 

(37)  B.t.u.    per   i.h.p.  hr.  =  Wsi(Htl  -  Hn) 

(38)  B.t.u.    per  b.h.p.  hr.  =  Wsh(Ha  -  Hi2) 

(39)  B.t.u.  per  i.h.p.  min.  =  WSi(Ht2  -  #z2)/60 

(40)  B.t.u.  per  b.h.p.  min.  =  Wsb(Hn  -  ff,2)/60 

See  the  author's  STEAM  TURBINE  PRINCIPLES  AND  PRACTICE  for 
discussion  of  the  reasons  for  expressing  the  performance  of  the  steam 
engines  and  turbines  in  so  many  different  ways,  and  for  an  explanation 
of  the  significance  of  "and  relationship  between  the  Rankine-cycle 
efficiency,  Rankine-cycle  ratio,  and  thermal  efficiency. 

NOTE. — THE  FOLLOWING  TABLES  SHOW  EFFICIENCIES  AND  PER- 
FORMANCE OF  STEAM  ENGINES  UNDER  VARIOUS  OPERATING  CONDITIONS. 
These  tables  are  taken  from  Gebhardt's  STEAM  POWER  PLANT  ENGINEER- 
ING published  by  John  Wiley  and  Sons,  New  York. 


312    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  10 


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Peabody,  Thermodynamics  
Peabody,  Thermodynamics  
Trans.  A.S.  M.E.,  Vol.  14,  p.  826 
Shop  test  
Elec.  World,  Sept.  1,  1904,  p.  407. 
Elec.  World,  Oct.  1,  1904,  p.  587.  . 
Eng.  Record,  July  6,  1901,  p.  7.  .  . 
Meyer,  Steam  Power  Plants,  p.  56 
Locomotive  Tests,  1904,  at 
Louisiana  Exposition  
Elec.  World,  Sept.,  1904,  p.  407.  .. 

s 

1 

Peabody,  Thermodynamics  
Elec.  World,  Oct.  1,  1904,  p.  587.  . 
Elec.  World,  Sept.  10,  1904 
p.  407  
Barrus,  Engine  Tests,  p.  95  

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SEC.  324] 


STEAM-ENGINE  EFFICIENCIES 


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Peabody,  Thermodynamics  

Corliss,  jacketed  

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Gridiron  valves  

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314     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  10 
325.  Table  Showing  Economies  Of  Multi-Expansion  En- 


Kind  of  engine 

References 

Cylinder 
dimensions 

Quadruple 


Nordburg   pumping   engine, 
Wildwood,  Pa. 


Eng.  News,  May  4,  1899,  p.  280 


29,  49 1- 
X  42 


Triple 


Allis  pumping  engine,  Chestnut 

Eng.    News,    Aug.    23,    1909, 

30,56,87  X  66 

Hill,  Boston. 

p.  125 

Allis    pumping    engine,    Bissel's 

Point,  St.  Louis  

Power,  May,  1906,  p.  299  

34,  62,  94  X  72 

Holly     pumping     engine,     Spot 

Eng.    News,    Nov.    14,    1901, 

22,  41,  62  X  60 

Pond,  Boston. 

p.  371. 

Sulzer  mill  engine,  Augsburg.  .  .  . 

Zeit.  d.  V.D.I.,  May  16,  1896, 

29.9,  44.5,  2(51.6) 

p.  534. 

X  78.7 

Compound, 


Allis-Chalmers     engines,     New 
York  Subway  

Power,  Feb.,  1906,  p.  115  

2(42),  2(86)  X  60 

Cross-compound     Corliss,      At- 
lantic Mills,  Providence  
Leavitt   puming   engine,   Louis- 
ville, Ky. 
Rice  &  Sargent  Corliss,   Amer. 
Sugar  Refinery,  Brooklyn. 
Fleming  four-valve. 

Williams    Vertical,    New    York 
Navy  Yard 

Am.  Elecn.,  June,  1903,  p.  260. 
Trans.     A.S.M.E.,      Vol.      16, 
p.  169. 
Trans.      A.S.M.E.,     Vol.      24, 
p.  1274. 
Trans.     A.    S.M.E.,    Vol.    25, 
p.  212. 

Power   Oct  ,  1903,  p   583     . 

16,  40  X  48 
27,  54  X  120 

20,  40  X  42 
15,  40H   X  27 

19,  34  X  30 

Tandem-compound  Corliss  
Edison  Waterside  Sta.,  N.  Y  

Barrus,  Eng.  Tests,  p.  185  
Power,  July,  1904,  p.  24  

18,  44  X  72 
43>£,  75.3  X  60 

Compound, 


Ball  &  Wood  Co.  Corliss,  W.  Al- 
bany Sta.,  N.  Y.  C.  &  H.  R.  R. 

Willans 

Willans 

Ball  engines,  Chicago  Public 
Library. 

Westinghouse  Marine 

Skinner  cross-compound 

Buffalo  tandem-compound. 

Reeves  vert,  cross-compound. . . . 

Cross-comp'd,  4  slide  valves 

4-cylinder  compound  locomo- 
tive No.  2512  Penna.  System. 


Test  by  Company  Engineers. .  . 

Peabody,  Thermodynamics.  . . . 

Peabody,  Thermodynamics.  .  .  . 

Eng.  Record,  Aug.  6,  1898, 
p.  206. 

Power,  Aug.,  1903 

Power,  July,  1906 

Elec,  World,  May  23,  1903, 
p.  897. 

Eng.  Record,  July  1,  1905,  p.  24 

Barrus,  Eng.  Tests,  p.  181 

Tests  made  at  Louisiana  Ex- 
position, 1904 


21,  41  X  30 
10,  14  X  6 
10,  14  X  6 
12,  20  X  13 

17,  27  X  24 
16,  27  X  18 
12,  18  X  10 

12,  20  X  14 

17M,  28  X  48 

14.2,  23.7  X  25.2 


*  Combined  efficiency  of  pump  and  engine. 

t  Cnmhinprt  p.ff\r,\p.nr,v  nf  fincrinp  and  ETfinerator. 


SEC.  325]  STEAM-ENGINE  EFFICIENCIES 

gines  Operating  On  Saturated  Steam. 


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158 

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11.96 

220.0 

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159 

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80.0 
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222.0 
222.0 

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19.0 

141 
150 

63.5 
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0.85 

121.0 

19.4 

121.0 

12.10 

222.7 

19.0 

143 

64.3 

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348.0 

150.0 

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152.0 

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126.0 

12.33 

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221.0 

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401.0 

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540.0 

148.0 

Atmos. 

210.0 

37.1 

1 

S 

19.3 

326.0 

13.0 

244 

75.0 

*87.5 

1:2.84 

375.0 

130.0 

Atmos. 

226.0 

31.0 

0 

u 

21.14 

355.0 

11.9 

255 

72.0 

91.5 

1:2K 

121.0 

128.0 

Atmos. 

271.0 

35.0 

1 

22.3 

376.0 

11.2 

258 

68.5 

93.0 

1:2.77 

185.0 

150.0 

Atmos. 

56.0 

1 

20.9 

354.0 

11.9 

242 

68.5 

92.0 

1:2.58 

486.7J125.3 

Atmos. 

99.0 

32.9 

S 

3 

21.59 

362.0 

11.7 

260 

71.9 

1:2.78 

495.0 

210.0 

Atmos. 

80.0 

55.0 

J 

18.6 

316.0 

13.4 

216 

68.5 

91.0 

316    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  10 
326.  Table  Showing  Economy  Of  Engines  Of  Various  Kinds 


Kind  of  engine 

References 

Cylinder 
dimensions, 
inches 

Triple 

Binary  vapor  eng.,  Royal  High 
School,  Berlin. 
Sulzer,  four-cylinder  
Sulzer,  three-cylinder  

Sulzer,  three-cylinder  

Jour.  Franklin  Inst.,  Dec.,  1902, 
p.  456. 
Eng.  News,  Oct.  2,  1902,  p.  259.  .. 
Zeit.    d.    V.    D.    I.,    Aug.,    1905, 
p.  1353. 
Engr.,    Lond.,     May    25,     1900, 

32,  47,  58  X  59 
15.5,  25.4,  37.5 
X  25.6 
34,  46,  61   X  51 

Worthington      pumping      eng., 

p.  546. 

Eng  News   May  26   1904  p  287 

Riedler    pumping    engine,    Chi- 
cago Ave.  Sta.,  Chicago. 

Engr.     U.    S.,     Nov.     15,     1907, 
p.  1092. 

15,  29,  48  X  48 

Compound 

Cole,     Marchent    and    Morley, 
cross-comp.,  jacketed. 
Van     den     Kerchove,     tandem, 
heads  jacketed. 
Van     den     Kerchove,     tandem, 
Heads  jacketed. 
Easton     &     Co.,     tandem-com- 
pound. 
Rice    and    Sargent,    Melbourne 
Mills,  Pa. 
Mclntosh  and  Seymour,  Edison 
Co.,  So.  Boston. 
Cross-compound,  cylinders  jack- 
eted. 
Sulzer,  tandem-compound  

Engr.,      London,      June,      1905, 
p.  546. 
Amer.  Elecn.,  May,  1903,  p.  217. 

Amer.  Elecn.,  May,  1903,  p.  217.. 
Amer.  Elecn.,  Apr.,  1903,  p.  178.  . 

Trans.     A.S.M.E.,     Vol.     25,    p. 
278. 
Trans.     A.S.M.E.,     Vol.    25,     p. 
491. 
Barrus,  Eng.  Test,  p.  202  

Eng.  News,  Oct.  2,  1902,  p.  259.  . 

21,  36  X  36 
12.8,  22  X  33.4 
12.8,  22  X  33.4 
15,  24  X  48 
16,  28  X  42 
29,  60  X  56 
18,  48  X  48 
26.8,  47.2  X  67 

Trans  A  S  M  E  ,  Vol  28      

3,6     X  4  .  5 

Nordberg  cross-compound  

U.  S.  Metal  Refining  Co  

19,  44  X  42 

Simple 

Poppet-valve  condensing 

Zeit.    d     V     D.    I.,    Aug.,    1905, 

16.3  X  39.4 

Poppet-valve,  condensing  
Poppet-valve,  non-condensing.  .  . 

Ideal  Corliss  
Erie  City  Lentz  

p.  1310. 
Zeit.    d.    V.    D.    I.,    Aug.,    1905, 
p.  1310. 
Zeit.    d.    V.    D.    I.,    Aug.,    1905, 
p.  1310. 
Power,  Mar.  4,  1913  
F.  W.  Dean,  1913  

16.3  X  39.4 
16.3  X  39.4 

16  X  22 
19  X  21 

SEC.  326]  STEAM-ENGINE  EFFICIENCIES 

Using  Superheated  Steam. 


317 


I  $ 

a 

1 

a 

.  •£ 

« 

* 

aJ 

i2 

sfi  g 

"«  "a 

T3 

H3 

Cylinder 

1 

S,-s 

S 

| 

1 

*  £ 

S 

b 

j 

ft 

a 

ratio 

a 

? 

£ 

g 

.£  -a 

ft  .s 

•3  s- 

01     ft 

S5 

5 

a 

S 

.  a 

S    w 

13  °" 

a  u' 

1 
w 

'S  ^j 

i* 

rt 

J  '" 

|j 

l| 

1'^ 

II 

02 

P 

expansion 


211 

143.0 

4.5 

143.5 

8.60 

158.3 

26.8 

221.0 

590 

1:2.03:3.27 
1:2.64:5.9 

2860 
549 

173.0 
166.0 

2.0 
2.4 

85.0 
144.4 

8.97 
10.00 

187.7 
207.3 

22.6 
20.4 

73.5 
68.5 

230.0 
229.0 

606 
602 

1  :  2  .  08  :  3  :  22 

2940 

646 
590.0 

167.0 

146.8 
170.0 

1.6 

1.6 
2.6 

82.5 

18.6 
62.0 

9.58 

10.00 
9.73 

204.0 

196.0 
196.5 

20.8 

21.6 
21.6 

66.7 

72.5 
69.3 

264.0 

87.0 
166.0 

'637 

451 
542 



1:2:94 

145.5 

114.5 

1.72 

100.7 

8.58 

176.1 

24.0 

82.0 

202.0 

548 

1:2.97 

212 

131.0 

2.2 

127.0 

8.99 

- 

194.8 

21.7 

73.0 

342.0 

699 

1:2.97 

217.0 

129.5 

2.2 

127.0 

10.75 

218.2 

19.4 

69.1 

183.0 

339 

1:2.67 

239.0 

120.0 

2.0 

140.0 

9.00 

187.0 

22.6 

78.5 

240.0 

590 

1:3.06 

920.0 

142.0 

4.0 

102.0 

9.56 

188.3 

22.5 

72.2 

296.0 

638 

1:4.3 

2202.0 

158.0 

4.8 

98.0 

11.21 

209.0 

20.2 

79.8 

92.0 

462 

1:7.3 

659.0 

143.0 

3.4 

80.0 

11.89 

223.5 

19.0 

73.5 

40.0 

402 

1:3.1 
1:4.0 
1:5.4 

788.0 
40.0 
620.0 

116.0 
426.0 
155.0 

2.8 
Atmos. 
3.87 

65.0 
85.0 
100.0 

9.68 
11.96 
11.01 

207.2 
244.0 
212.0 

20.3 
17.4 
20.0 

71.5 
68.0 
75.3 

343.0 
316.0 
76.1 

690 
766 
444 

123.0 

145  0 

. 
1   4 

81    1 

16  70 

326  0 

13  0 

46  0 

73  8 

1' 

20.0 

145.0 

1.5 

81.2 

14.70 

307.4 

13.8 

47.6 

226.2 

5* 

123.0 
190  0 

145.0 
125  0 

Atmos. 

81.5 
200  0 

16.10 
18  3 

307.8 
328  0 

13.8 
13  0 

79.0 
78  5 

254.3 
107  0 

0( 

4i 

248  0 

133  0 

206  0 

16  1 

286  0 

14  8 

87  5 

92  7 

1 

318    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  10 

QUESTIONS  ON  DIVISION  10 

1.  Explain  why  only  a  small  part  of  the  total  theoretical  heat  contained  in  steam  may 
be  utilized  in  a  steam  engine. 

2.  Explain  why  the  greatest  thermal  efficiency  does  not  always  result  in  the  lowest 
total  power  cost. 

3.  Is  it  usually  possible  to  greatly  increase  the  efficiency  of  an  engine  which  is  already 
in  good  repair?     Why? 

4.  What  class  of  losses  in  a  steam  engine  tends  to  increase  at  over  loads?     What 
classes  are  proportionately  larger  at  light  loads? 

5.  Name  several  methods  of  decreasing  percentage  rejection  losses. 

6.  What    mainly   determines   the  boiler  pressure  which  is  ordinarily  used  for  steam 
engine  service? 

7.  What  are  three  principal  causes  of  cylinder  condensation? 

8.  Why  may  a  steam-engine  power  plant  be  practically  more  efficient  when  both  heat 
and  power  are  desired  than  when  the  steam  is  generated  for  power  purposes  only? 

9.  What  is  the  principal  method  of  reducing  thermal  losses  in  a  steam  engine? 

10..  What  method  of  reducing  mechanical  losses  is  applicable  to  an  existing  steam- 
engine  installation? 

11.  What  measures  are  taken  to  reduce  gland  friction?     Bearing  friction?     Piston 
friction? 

12.  Explain  by  a  diagram  the  relation  between  various  standards  of  engine  efficiency. 

13.  What  effect  on  efficiency  has  a  moderate  amount  of  water  in  the  steam  admitted 
to  a  steam  engine? 

14.  Why  is  engine  performance  compared  to  the  ideal  Rankine  cycle?     Name  one 
modification  of  the  original  ideal  Rankine  cycle  which  is  necessary  in  practice  but  which 
does  not  involve  a  loss.     One  which  does. 

15.  Explain  why  the  heat  of  liquid  at  the  temperature  of  the  engine  exhaust  is  taken 
as  a  basis  in  engine-efficiency  calculations. 

16.  What  is  the  Rankine-cycle  ratio  of  an  engine?     What  other  expressions  are  used 
to  designate  this  same  ratio? 

PROBLEMS  ON  DIVISION  10 

1.  What  is  the  efficiency  of  the  ideal  Rankine  cycle  operating  on  99  per  cent,  quality 
steam  at  200  Ib.  per  sq.  in.  abs.  and  exhausting  at  212  deg.  fahr? 

2.  What  is  the  theoretical  water  rate  of  an  engine  operating  on  steam  at  a  total 
temperature  of  550  deg.  fahr.  and  a  pressure  of  150  Ib.  per  sq.  in.  gage?     The  exhaust 
pressure  is  1.5  Ib.  per  sq.  in.  abs. 

3.  What  is  the  thermal  efficiency  of  an  engine  which  uses  18.5  Ib.  of  steam  per  indicated 
horse  power  hour  and  operates  on  98  per  cent,  quality  steam  at  175  Ib.  per  sq.  in.  abs., 
exhausting  at  atmospheric  pressure? 

4.  If  the  engine  in  Problem  1  uses  25  Ib.  of  steam  per  indicated  horse  power  hour,  what 
is  its  Rankine-cycle  ratio? 

6.   What  is  the  mechanical  efficiency  of  an  engine  which  delivers  175  brake  horse  power 
while  showing  198  i.h.p.? 

6.  What  is  the  over-all  efficiency  of  an  engine  which  uses  17.4  Ib.  of  steam  per  b.h.p. 
hr.?     The  steam  has  100  deg.  fahr.  superheat  at  178  Ib.  per  sq.  in.  abs.  and  is  exhausted 
into  a  condenser  which  has  27  in.  of  mercury  vacuum  when  the  barometer  reads  29.8  in. 

7.  How  many  British  thermal  units  per  brake  horse  power  are  used  by  the  engine  in 
Problem  6?     How  many  British  thermal  units  are  used  per  kilowatt  hour  of  mechanical 
power  developed? 

8.  Compare  the  thermal  efficiencies  of  two  engines — one  using  19  Ib.  of  steam  per 
indicated  horse  power  hour  at  125  Ib.  per  sq.  in.  abs.;  and  the  other  18  Ib.  at  225  Ib.  per 
sq.  in.  abs.      Both  exhaust  at  atmospheric  pressure  and  use  saturated  steam. 


DIVISION  11 
STEAM  ENGINES  OF  MODERN  TYPES 

327.  The  Material  Here  Given  On  "Steam  Engines  Of 
Modern  Types  "  (see  also  Table  337)  will  outline  the  principal 
constructional,  operating,  and  economic  characteristics  of  the 
different  types  of  modern  engines.     For  each  type  there  will, 
insofar  as  is  feasible,  be  given  information  relating  to  the  valves, 
their  control,  the  speed  in  revolutions  per  minute,  the  type 
of  governor,  particular  advantages,  performance,  and  initial 
cost    (Sec.   338).     This   information   must,   of  necessity,   be 
general  because  of  the  many  engines  in  each  class  and  their 
widely  different  characteristics.     It  is  hoped  that  this  infor- 
mation will  provide  a  suitable  basis  for  selecting  the  proper 
type  and  size  of  engine  for  a  given  service.     The  problems  of 
selection,  however,  will  be  discussed  in  Div.  15. 

328.  Rotary  Steam  Engines  (Fig.  373)  differ  from  recipro- 
cating engines  in  that  the  piston,  or  its  equivalent,  in  the 
rotary  engine  rotates  about  the  cylinder  axis.     The  steam 
pressure  forces  the  piston  around,  just  as  in  the  reciprocating 
engine  the  pressure  forces  the  piston  ahead.     In  this  way  the 
rotary  engine  differs  from  the  steam  turbine  because  in  the 
turbine  the  momentum  of  the  steam  is  imparted  to  the  rotat- 
ing member.     Rotary  engines  when  new  and  well  made  usually 
have  steam  rates  of  60  to  125  Ib.  per  i.h.p.  hr.     Since,  due  to 
their  construction,  it  is  difficult  to  take  up  wear  in  rotary 
engines,  and  since  the  chances  for  steam  leakages  are  exces- 
sive, rotary  engines,  after  they  are  used  for  a  short  time, 
consume  a  great  amount  of  steam  which  simply  passes  through 
the  engine  without  doing  work.     For  this  reason,  although 
they  possess  many  apparent  advantages,  rotary  engines  cannot 
compete  with  even  the  most  wasteful  reciprocating  engines. 
Since  they  do  not  constitute  a  class  of  commercially  useful 
steam  engines,  rotary  engines  will  not,  except  as  in  the  explana- 
tion below,  be  discussed  further  herein. 

319 


320     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  11 

EXPLANATION. — The  operation  of  the  rotary  steam  engine  is  illustrated 
in  Fig.  373.  Assume  that  at  the  instant  when  steam  is  admitted,  the 
piston,  AB,  stands  as  shown  in  7.  The  pressure  of  the  steam  acting  on 
A  exerts  a  force  which  is  indicated  by  the  small  arrows.  This  force  will 
rotate  the  rotor,  R,  to  which  A  is  secured.  After  position  II  is  reached, 
piston  B  automatically  closes  the  space  behind  A  so  that  no  more  steam 
is  admitted.  However,  steam  is  now  admitted  below  B.  The  steam 
above  AB  still  acts  on  piston  A  and  tends  to  rotate  R.  This  steam  will 
expand  slightly  as  R  rotates  from  position  II  until  AB  is  horizontal. 


- Release  At  A  E- Exhaust 

FIG.  373. — Illustrating  principle  of  the  rotary  steam  engine. 

Then,  however,  the  steam  above  AB  is  again  compressed  as  R  approaches 
position  III.  Here  A  is  about  to  open  the  passage  for  the  steam  into  the 
outlet.  Position  IV  shows  the  steam  exhausting  from  the  cylinder. 
It  is  evident  that  in  this  engine  work  is  done  by  the  steam  by  virtue 
of  direct  pressure  only — :there  is  practically  no  expansion.  It  is  obvious 
also  that  unless  a  tight  joint  is  kept  between  the  cylinder  and  rotor  at  C, 
positions  II,  III,  and  IV,  steam  can  blow  from  the  inlet  to  the  outlet 
pipe  without  doing  any  work.  The  difficulty  of  keeping  tight  joints 
at  C  and  at  the  ends  of  the  pistons  is  the  most  objectionable  feature  of  the 
rotary  engine. 


SEC.  329]       STEAM  ENGINES  OF  MODERN  TYPES 


321 


329.  Simple  Single -Valve  Engines  (Fig.  374)  are  onade  in 
a  great  number  of  styles  in  sizes  from  2  to  900  h.p.;  see  Table 
337.  The  speeds  vary  from  about  600  to  150  r.p.m. ;  the  piston 
speed,  however,  remains  nearly  the  same  for  all  engines — 


about  600  feet  per  minute  (f.p.m.)  being  an  average  value, 
although  800  f.p.m.  is  not  uncommon.  These  engines  are 
usually  fitted  with  either  piston  (Fig.  375)  or  balanced  slide 
valves  except  that,  in  the  very  small  sizes,  plain  D-slide  valves 
are  sometimes  used;  see  Table  337.  Simple  single-valve 
engines  usually  operate  on  steam  at  pressures  below  125  Ib. 
21 


322-    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  11 


per  sq.   in.   gage,  and  no  more  than  50  deg.  of  superheat, 
although  the  piston-valve  engines  may  safely  be  used  with 


Steam 


Steam 
Chest^ 


Va/ve 
Stem, 


-'IftiaStroke-IOOLb.  Per  S^InGaep  — 
)8in.Stroke-ISO»    ' 


'Cylinder   ^piston  ^Steam    Piston  ,' 
Head  Supply         Rod 

FIG.  375. — Section  of  cylinder  of  a 
piston-valve  engine.  (Arrows  indicate 
direction  of  steam  flow.) 


0         15        50         75         100      125 
Per  Cent  Of  Rated  Load 

FIG.  376. — Typical  steam  consumption 
curves  for  good,  simple  high-speed  engines 
non-condensing. 


temperatures    up    to    570    deg.    fahr.     Simple    single-valve 
engines  may  be  obtained,  usually,  with  either  throttling  or 


Hydrostatic 
Lubricator. 

Steam 
Oage- 


Safety 
Valve, 


--Throttling 


FIG.  377. — Typical  small  portable  boiler  and  engine  unit.     (Ames  Iron  Works.) 

shaft  governors.  They  are  seldom  operated  condensing; 
in  fact,  they  are  most  widely  used  where  fuel  is  very  cheap  or 
where  large  quantities  of  exhaust  steam  are  needed  for  heating 


SEC.  330]       STEAM  ENGINES  OF  MODERN  TYPES  323 

or  manufacturing  purposes.  They  are  compact,  simple  in 
construction  and  operation,  and  low  in  first  cost.  As  is 
shown  by  Fig.  376,  the  steam  consumption  varies  little  at 
loads  ranging  from  50  to  125  per  cent,  of  rated  full  load, 
but  is  much  higher  at  small  fractional  loads.  At  full  load,  the 
steam  consumption  varies  for  different  engines  from  26  to  50 
Ib.  per  i.h.p.  hr.  depending  on  the  cylinder  size  and  initial 
steam  pressure.  A  good  average  value  may  be  taken  as 
30  Ib.  per  i.h.p.  hr.  The  most  advisable  cut-off  when  running 
non-condensing  is  about  Y%  to  Y±  stroke. 

NOTE. — PORTABLE  SLIDE-VALVE  ENGINES  are  those  which  are  intended 
for  use:  (1)  Upon  a  portable  boiler  which  may  be  mounted  on  skids  (Fig. 
377)  or  on  wheels.  (2)  Upon  only  a  temporary  foundation  which  is  usually 
made  of  timbers.  A  portable  engine  is  usually  furnished  with  a  portable 
boiler — the  two  form  a  small  portable  power  plant.  Portable  engine 
and  boiler  units  are  built  in  sizes  up  to  about  75  h.p. 

330.  Compound  Single-Valve  Engines  (Fig.  378)  are  gen- 
erally used  where,  during  a  part  of  the  year,  their  exhaust  is  to 

..High -pressure  Cylinder 
.-Distance  Piece 

.-Low-pressure  Cylinder 


055? 

FIG.  378. — Longitudinal   section   of   a   typical   high-speed   tandem-compound   engine. 

be  used  for  heating,  but  at  other  times  they  are  to  operate 
condensing.  They  are  also  often  used  where  the  initial  steam 
pressure  is  over  125  Ib.  per  sq.  in.  The  steam  pressure  at  the 
throttle  may  run  as  high  as  200  Ib.  per  sq.  in.  but  the  tempera- 
ture should  not  exceed  400  deg.  fahr.,  with  flat  slide  valves. 
Compound  single-valve  engines  are  nearly  always  equipped 
with  shaft  governors  which  regulate  the  steam  supply  to  the 
high-pressure  cylinder,  whereas  the  low-pressure  cylinder  has 
its  valve  driven  from  a  fixed  eccentric.  Compound  single- 
valve  engines  are  generally  built  in  both  tandem  and  cross 
types  and  in  sizes  up  to  1200  h.p. ;  see  Table  337.  Figs.  379  to 


324     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  11 


381  show  the  steam  consumption  for  these  engines.  An 
attempt  has  been  made  to  show  the  effects  of  initial  steam 
pressure,  back  pressure,  and  cylinder  size.  The  piston  speeds 
are  again  about  600  f.p.m. 

45 
i  40 


1 

\\H 

rtton-C 

ondens 

ing 

*\ 

V-rA 

Sjgg 

. 

^Condensing 

100         25        50        75"     100      125 

Per  Cent  Of  Rated  Load 
FIG.  379. — Typical  steam  consumption 
curves  for  cross-  and  tandem-compound 
engines  using  steam  at  100  Ib.  per  sq.  in. 
gage.  The  full  lines  are  for  an  engine  of 
36-in.  stroke  whereas  the  dashed  lines  are 
for  one  of  18-in.  stroke. 


25         50         75         100      l?5 
Per  Cent.  Of  Rated  Load 

FIG.  380. — Typical  steam-consumption 
curves  for  cross-  and  tandem-compound 
engines  using  steam  at  150  Ib.  per  sq.  in. 
gage.  The  full  lines  are  for  engines  of 
36-in.  stroke  whereas  the  dashed  lines 
represent  engines  of  18-in.  stroke. 


331.  Engines  With  Riding-Cut-Off  Valves  (Fig.  184), 
although  once  quite  popular,  are  not  widely  built  today. 
While  these  engines  have  their  advantages  (Sec.  141),  their 

economy  is  little  better  than  that 
of  single-valve  engines.  Engines 
with  riding-cut-off  valves  are  built 
simple  and  compound  and  in  sizes 
up  to  2000  h.p.  (see  Table  337). 
They  may  have  plate  (Fig.  184) 
'o — 75  so  75  100  12  °r  piston  (Fig.  185)  valves. 

Per  cent,  of  Rated  Load  332.  Four-Valve  Engines  (Fig. 

FIG.  381. -Typical  steam-con-  335  and  g^  -^  are  being  made 
sumption  rates  for  high-speed,  *  c 

tandem-compound    engines.    Full    m  a  large  number  of  forms  by 

lines  represent  condensing  operation  Different  engine  builders;  S6C 
with  150  Ib.  per  sq.  in.  pressure  at  ° 

throttle  and  26-in.  vacuum.    Dotted    Table  337.     The  valves  may  be 

lines   denote  the  same  with  100  Ib.  Qf    the    piston    (fig.    382)      Corliss 

steam  pressure.     Dashed  lines  refer  r 

to     non-condensing    operation    with  (Fig.    238),    Or    poppet   type    (Fig. 

steam  at  150  Ib.  per  sq.  in.  by  gage.  223).       The       Mclntosh       &      Sey- 

mour  engine  with  four  flat  slide  (gridiron)  valves  (Sec. 
142)  is  no  longer  manufactured.  The  poppet-valve  engines 
may  be  of  the  so-called  "uniflow"  (Sec.  334)  or  of  the 


SEC.    332]      STEAM  ENGINES  OF  MODERN  TYPES 


325 


320     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  11 


SEC.  332]       STEAM  ENGINES  OF  MODERN  TYPES 


327 


"full-poppet"  type  (Figs.  383  and  384).  Strictly  speaking, 
the  four-valve  uniflow  engine  does  not  operate  on  the  original 
uniflow  principle,  because  some  steam  is  exhausted  through 
auxiliary  exhaust  valves  (see  Sec.  334).  Four-valve  engines 
of  all  types  (except  the  "uniflow"  type)  are  built  both  simple 


Roller-. 


FIG.  384. — Transverse  section  through  valves  of    "Lentz"   engine.     (Erie  City   Iron 

Works.) 

and  compound.  Nearly  all  of  the  detaching  Corliss-valve 
engines  (see  Div.  5)  are  equipped  with  fly-ball  governors. 
All  others  most  often  have  centrifugal-inertia  or  shaft  gover- 
nors. Four-valve  engines,  as  a  class,  have,  as  stated  below, 
low  steam  rates  as  is  shown  by  Figs.  385  to  388.  See  Sec.  428 
for  allowable  pressures  and  superheats  for  these  engines. 


328    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  11 

NOTE. — SIMPLE  FOUR-VALVE  (CORLISS)  ENGINE  STEAM  RATES 
(see  Fig.  207  for  a  picture  of  such  an  engine),  at  full  load,  vary  from  about 
22  to  27  Ib.  per  i.h.p.  hr.  when  operating  non-condensing  and  supplied 


0          75         50         15         100      175 
Per  Cent.  Of  Rated  Load 

FIG.  385. — Typical  steam-  consumption 
curves  for  simple,  non-condensing  four- 
valve  engines.  Full  lines  represent  rates 
for  engines  supplied  with  steam  at  150  Ib. 
per  sq.  in.  gage.  Dashed  lines  refer  to  oper- 
ation on  steam  at  100  Ib.  per  sq.  in.  gage. 


0         25         50         75         100      175 
Per  Cent.  Of  Rated   Load 

FIG.  386. — Typical  steam-consump- 
tion curves  for  compound  four-valve 
engines  operating  non-condensing. 
Full  lines  represent  rates  for  engine 
supplied  with  steam  at  150  Ib.  per  sq. 
in.  gage.  Dashed  lines  refer  to  operation 
on  steam  at  100  Ib.  per  sq.  in.  gage. 


with  steam  at  125  to  140  Ib.  per  sq.  in.  gage.  With  superheated  steam 
the  steam  rate  may  be  only  about  17  Ib.  per  i.h.p.  hr.  Typical  indicator 
diagrams  from  a  simple  non-releasing  Corliss  engine  are  shown  in  Fig.  389. 


0         75        50         75        100      125 
Per  Cent.  Of  Rated  Load 

FIG.  387. — Typical  steam  consump- 
tion curves  for  compound  four-valve 
engines  operating  condensing  with  a 
26-in.  vacuum.  Full  lines  represent 
rates  for  engines  supplied  with  steam 
at  150  Ib.  per  sq.  in.  gage.  Dashed 
lines  refer  to  operation  on  steam  at  100 
Ib.  per  sq.  in.  gage. 


15        50        Ib         100      125 
Per   Cent.  Of  Rated  Load 

FIG.  388. — Typical  steam-consump- 
tion curves  for  single-cylinder  poppet- 
four-valve  engines  of  18-in.  stroke  when 
supplied  with  steam  at  100  Ib.  per  sq.  in. 
gage.  Full  lines  represent  results  with 
saturated  steam;  dashed  lines  corres- 
pond to  100  deg.  fahr.  of  superheat; 
dotted  lines  correspond  to  200  deg.  fahr. 
of  superheat. 


The  poppet-valve  engine  seems  to  be  more  economical  than  the  Corliss. 
Tests  have  shown  non-condensing  poppet-valve  engines  to  operate  on 
as  little  as  18.9  Ib.  of  saturated  steam  per  i.h.p.  hr.;  and,  with  superheated 


SEC.  332]       STEAM  ENGINES  OF  MODERN  TYPES 


329 


steam  (150  Ib.  per  sq.  in.  gage  and  250  deg.  fahr.),  it  is  not  unusual  to 
get  as  low  as  16  Ib.  per  i.h.p.  hr. 

NOTE.  —  THE  STEAM  RATES  OF 
COMPOUND  FOUR- VALVE  ENGINES 
(Fig.  390)  at  full  load  when  oper- 
ating non-condensing  range  from  17 
to  22  Ib.  per  i.h.p.  hr.;  with  saturated 
steam,  and  as  low  as  12  Ib.  per  i.h.p. 
hr.  with  superheated  steam.  When 
operated  condensing  the  steam  rate 
may  be  as  low  as  12  Ib.  per  i.h.p.  hr., 
on  saturated  steam,  whereas  with 
superheated  steam  it  has  been  re- 
duced (see  Table  326)  to  about  9  Ib.; 
these,  however,  are  exceptional  values  and  are,  perhaps,  20  per  cent, 
below  good  average  practice. 

NOTE.— FOUR- VALVE  "UNIFLOW"  ENGINES  (Figs.  224,  225,  and  486) 


FIG.  389. — Actual  indicator  diagrams 
from  a  14  by  21-in.  Chuse  non-releasing 
Corliss  engine  in  the  Rice-Stix  Dry 
Goods  Co.  plant  in  St.  Louis.  Operat- 
ing conditions  when  diagrams  were 
taken  follow:  Initial  steam  pressure, 
160  Ib.  per  sq.  in.  Exhaust,  atmos- 
pheric. Speed,  230  r.p.m. 


High-Pressure  Cylinder. 


I  -  Plot  n  V  iew      '  "Low-Pressure 
Cylinder 


I-End  Elevation 


•  /  '"Engine-Room\ 
"  ***•>  -'•  - .-'" '         Floor  Line 
,-Anchor-Plate  .•    Foundation  '. 


wy//JD/wI^ 


~28" Exhaust 
Pipe 


Hi-Side  Elevation 

FIG.  390. — Assembly  drawing  of  a  cross-compound  Fulton-Corliss  steam  engine.     The 
cylinders  are  36  and  76  in.  in  diameter.     The  stroke  is  54  in. 


are  generally  constructed  for  non-condensing  service.  Although  most 
of  the  used  steam  is  exhausted  at  the  end  of  the  forward  stroke  through 
the  central  exhaust  holes  in  the  cylinder  wall,  more  steam  is  exhausted 


330     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.   11 


SEC.  333]       STEAM  ENGINES  OF  MODERN  TYPES 


331 


during  the  return  stroke  through  auxiliary  exhaust  valves.  Although 
such  an  engine  is  not  truly  of  the  uniflow  type,  its  economy  (Fig.  392) 
is  generally  somewhat  better  than  that  of  an  engine  operating  on  the 
true  counter-flow  principle. 

333.  The  Uniflow  Engine  (Sees.  59  and  434  and  Fig.  391), 
as  originally  invented,  was  intended  to  be  operated  condensing 
and  to  have  no  exhaust  valves.  The  expanded  steam  should 
be  exhausted  through  the  central  port-holes  in  the  cylinder 
when  these  holes  are  uncovered  by  the  piston.  When  these 
holes  are  again  covered  by  the  returning  piston,  the  unex- 
hausted steam  within  the  cylinder  (at  condenser  pressure  of 
1  to  2  Ib.  per  sq.  in.  abs.)  is  compressed.  Since  the  compression 
period  is  long  and  the  clearance  small,  the  unrejected  steam  is 


Lb.  Steam 
Perl.H.P-Hr 

D  Cn  o  Cn  O 

Not 

-j-Conct 

?ns/ngr 

hi  —  • 

( 

'onden 

sing--. 

\ 

r: 


"0         25        50        Ib        100      125 
Per  Cent  Of  Rated  Load 

FIG.  392. — Steam-consumption  curves 
for  a  21  by  22  in.  Skinner  "Universal 
Unaflow"  engine  supplied  with  saturated 
steam  at  140  Ib.  per  sq.  in.  gage. 


FIG.  393. — Actual  indicator  diagrams 
from  a  20  by  24-in.  Chuse  condensing 
uniflow  engine  at  the  Holstead  Mill  and 
Elevator  Co.,  Holstead,  Kan.  The  operat- 
ing conditions  under  which  these  diagrams 
were  taken  are:  Steam  supplied  at  150 
Ib.  per  sq.  in.  Vacuum  in  condenser,  23 
in.  Speed  200  r.p.m. 


compressed  to  a  high  pressure — usually  the  pressure  at  the 
throttle.  The  cylinder  heads  are  jacketed  with  high  tempera- 
ture steam.  Thus  the  unrejected  steam  is  superheated  during 
its  compression.  Because  of  this  fact  and  because  the  colder 
exhaust  steam  does  not  sweep  over  the  warm  surfaces  near  the 
heads,  cylinder  condensation  is  much  less  in  this  engine  than 
in  a  counter-flow  engine.  Also  it  has  been  found  that  the 
ratio  of  expansions  within  the  cylinder  can  be  varied  widely 
without  appreciably  affecting  the  economy.  This  accounts 
for  the  small  difference  (Fig.  392)  in  the  uniflow  steam  rates 
between  full  load  and  small  fractional  loads  or  large  over- 
loads. Since  the  normal  cut-off  is  usually  about  Jf  o  to  J£ 
stroke,  uniflow  engines  are  capable  of  large  over  loads.  Fig. 


332     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  11 

393  shows  typical  indicator  diagrams.  With  saturated  steam 
at  moderate  pressure  the  steam  rates  are  about  12  to  15  Ib. 
per  i.h.p.  hr.  With  higher  pressures  and  superheat  still 
better  economy  can  be  obtained.  The  record,  it  seems,  is 
reported  by  Lentz  as  5.67  Ib.  per  i.h.p.  hr.  with  steam  at  461 
Ib.  per  sq.  in.  abs.  and  superheated  by  495  deg.  to  1,018  deg. 
fahr. 

334.  Non-Condensing  Uniflow  Engines  must,  of  necessity, 
be  built  differently  from  those  which  are  designed  to  operate 
only  condensing.  Modern  uniflow  engines  are  frequently 
designed  so  that  they  may  be  operated  either  condensing  or 
non-condensing.  A  uniflow  engine  designed  solely  for 
condensing  operation,  if  operated  non-condensing  would 
compress  steam  from  a  pressure  of  about  15  Ib.  per  sq.  in.  abs. 
instead  of  from  1  or  2  Ib.  The  result  would  be  that,  if  no 
provision  were  made  to  prevent  it,  the  pressure  in  the  engine 
cylinder  would  rise  during  compression  to  many  times  the 
pressure  of  the  incoming  steam.  To  prevent  this  excessive 
pressure  (which  would  probably  cause  rupture  of  the  cylinder) 

several  schemes  are  employed. 
(1)  The  clearance  volume  may  be 
increased  so  that  a  much  greater 
space  is  provided  to  store  the 
^  compressed  steam ;  engines  which 

Atmospheric  Pressure-----.-*  .-.'•:•::'.'.•  \ 

are   to  be  operated  either  con- 

FIG.  394. — Actual  indicator  diagrams       .    '      .  , 

from  a  23  by  28-in.  chuse  non-condens-  densmg  or  non-condensing  are 
ing  uniflow  engine  at  Bridge  &  Beach  equipped  with  a  small  clearance 

Mfg.  Co.,  St.  Louis.     These  diagrams      -  ,  ,  .  ,  .    , 

taken  while  the  operating  condi-     for    Condensing   Operation   which 


were 


tions    were:     Initial     steam    pressure,      may    be     Connected     by    Opening 
160   Ib.    per   sq.   in.     Exhaust,  atmos-  ,  .,,  jj-o.-          i 

speed  150  r.p.m.  a     valve     with     an     additional 


space  to  provide  the   necessary 

clearance  for  non-condensing  operation  —  the  valve  may  be 
automatic  (Fig.  244)  or  hand-operated.  (2)  Auxiliary  exhaust 
valves  may  be  employed  to  continue  the  exhaust  period  during 
a  portion  of  the  return  stroke  after  the  main  exhaust  ports 
are  covered  by  the  piston;  these  valves  may  connect  into 
the  cylinder  at  the  end  (Fig.  486)  or  into  the  wall  some- 
where between  the  center  and  end  of  the  cylinder  (Fig.  224). 
Typical  indicator  diagrams  from  an  engine  which  has 


SEC.  335]       STEAM  ENGINES  OF  MODERN  TYPES  333 

auxiliary  exhaust  valves  are  shown  in  Fig.  394.  Engines 
of  this  type  which  are  to  be  operated  either  condensing  or 
non-condensing  are  generally  fitted  with  some  means,  auto- 
matic or  manual,  for  keeping  the  auxiliary  valves  closed  when 
operating  condensing.  (3)  The  admission  valves  may  be  lifted 
from  their  seats  or  relief  valves  set  to  open  when  the  pressure 
within  the  cylinder  becomes  excessive — thus  allowing  steam 
to  escape  from  the  cylinder.  This  means  of  adapting  a 
condensing  engine  to  non-condensing  operation  is  necessary 
as  a  safety  measure  but  is  wasteful  and,  therefore,  is  not 
employed  during  regular  running. 

NOTE. — THE  ECONOMY  OP  NON-CONDENSING  UNIFLOW  ENGINES  varies 
somewhat  with  the  design,  but  with  saturated  steam  at  moderate 
pressures  (125  to  150  Ib.  per  sq.  in.  gage)  steam  rates  of  18  to  25  Ib. 
per  i.h.p.  hr.  may  be  expected  at  full  load.  At  partial  loads  and 
overloads,  the  steam  rates  increase  more  rapidly  than  for  condensing 
uniflow  engines  but  still  not  as  rapidly  as  for  counterflow  engines.  Non- 
condensing  uniflow  engines  have  been  run  at  250  per  cent,  of  their 
rated  load  with  only  a  25  per  cent,  greater  steam  rate  than  at  rated  full 
load.  The  costs  of  these  engines  are  given  in  Sec.  338.  They  may  be 
safely  operated  on  steam  at  any  pressure  and  temperature  so  long  as 
effective  lubrication  can  be  maintained  (see  Sec.  430). 

335.  The    "Locomobile"    Is    A   Type    Of    Steam    Engine 

(Fig.  395)  which  is  built  integral  with  a  boiler  which  supplies 
its  steam.  It  was  first  made  in  Germany  under  the  name 
"lokomobile."  Many  of  these  units  have  long  been  in  use  in 
Europe  but,  until  recently,  few  have  been  used  in  this  country. 
The  engine  is  mounted  above  the  boiler  and  the  flue  gases  are 
used  to  jacket  the  cylinders.  Steam  is  usually  generated  at  a 
high  pressure  and  superheated.  The  entire  unit  is  so  designed 
that  its  efficiency  can  be  maintained  very  high.  The  loco- 
mobile type  of  power  plant  is  manufactured  in  this  country 
under  the  name  Buckeye-mobile  (see  Table  337)  which  is 
illustrated  in  Fig.  395.  The  engine  is  a  tandem-compound 
with  piston  valves;  the  receiver  is  placed  in  the  flue-gas  path 
and  arranged  as  a  reheater.  Typical  performance  graphs  are 
shown  in  Fig.  396.  By  reason  of  its  exceptionally  good  econ- 
omy, the  locomobile  is  very  well  suited  for  small  power  plants 
where  good  boiler  water  is  scarce  and  where  fuel  is  expensive. 


334     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    (Div  11 


336.  Steam-Engine  First  Cost  Is  Influenced  By  Many 
Factors. — In  a  general  way,  the  cost  of  an  engine  depends  on 
its  cylinder  dimensions  and  the  maximum  pressure  which  the 


SEC.  336]       STEAM  ENGINES  OF  MODERN  TYPES 


335 


cylinder  will  sustain.  But,  to  establish  some  relation  between 
cost  and  the  power  which  the  engine  will  develop — that  is, 
to  attempt  to  predict  the  exact  cost  of  an  engine  of  a  certain 
class  and  horse  power — is  almost  impossible  because  of  the 
many  influencing  factors:  (1)  Initial  steam  pressure  deter- 
mines the  power  which  an  engine  will  develop — an  engine  of  a 
given  size  (and  cost)  will  therefore  give  most  power  when 
supplied  with  steam  at  the  maximum  pressure  for  which  it  is 


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FIG.  396. — Performance  graphs  of  a  150-h.p.  Buckeye-mobile.     Fuel  was  Pocahontas 
run  of  mine,  14,000  B.t.u.  per  Ib.     (Buckeye  Engine  Co.) 

safe.  (2)  Speed,  in  revolutions  per  minute,  likewise  affects 
the  power  output — an  engine  of  a  given  size  (and  cost)  will 
therefore  deliver  most  power  when  operated  nearest  its 
rated  maximum  speed.  (3)  Back  pressure  likewise  affects  the 
power  output —  the  lower  the  back  pressure,  or  if  condensing, 
the  greater  the  vacuum,  the  greater  will  be  the  power  output. 
(4)  The  service  for  which  the  engine  is  to  be  used  affects  the 
necessary  construction — engines  for  driving  alternating- 
current  generators  must  have  larger  flywheels  than  those  for 
some  other  services;  engines  for  direct  connection  to  electric 
generators  usually  require  longer  shafts  and  different  bearing 
constructions  than  do  those  which  are  to  drive  by  belt  or 
rope;  some  engines  must  be  designed  to  operate  at  variable 
speeds,  some  to  be  readily  reversed.  (5)  Sub-bases  are  some- 
times required  by  the  purchaser — sometimes  they  are  not. 
When  required,  sub-bases  must  sometimes  have  special 
construction. 


336    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  11 


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340     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  11 


NOTE. — VARIABLE  SPEED  AND  REVERSING  ENGINES  arc  also  manu- 
factured by  many  of  the  engine  builders  listed  in  Table  337  but  these 
engines  are  not  listed  in  the  above  table. 

EXPLANATION. — TABLE  337,  although  it  was  intended  to  contain  the 
names  and  descriptions  of  the  principal  engines  manufactured  in  this 
country,  must  be  understood  to  possibly  not  include  all  such  engines. 
Furthermore,  the  fact  that  a  certain  engine  is  or  is  not  included  in  this 
table  should  not  be  taken  to  indicate  anything  whatever  with  regard 
to  its  merits  or  quality. 

338.  Table  Of  Costs  Of  Steam  Engines  Of  Different 
Types. — The  costs  given  below  must  be  understood  to  be 
merely  approximate  prices  and,  because  of  fluctuations  in  the 
market  and  the  factors  explained  in  the  preceding  section, 
should  be  used  only  in  making  a  preliminary  estimate.  For  a 
final  (or  even  for  a  reasonably  accurate  preliminary)  estimate, 
prices  should  be  obtained  from  the  engine  manufacturers. 
The  prices  given  below  are  as  of  January  1,  1922,  for  engines 
without  special  bases  and  arranged  for  belt  drive  from  the 
flywheel. 


Type  of  engine 

Cost  of  engine  per  horse  power 

Small  engine 

Large  engine 

Simple  slide-valve  
Compound  slide-valve               .... 

$22-44 
22-33 
25-37 
35-45 
32-45 

$11-16 
15-17 
9-18 
16-25 
12-21 

Simple  four-valve 

Compound  four-valve  
Uniflow  .  . 

QUESTIONS  ON  DIVISION  11 

1.  Explain  the  differences  between  rotary  steam  engines  and  (1 )  reciprocating  engines 
(2)  steam  turbines. 

2.  Explain,  with  a  sketch,  the  operation  of  a  rotary  steam  engine.     What  are  its  short- 
comings?    Is  it  widely  used? 

3.  What  are  the  usual  sizes  and  rotative  speeds  of  simple  single-valve  engines?     What 
is  their  field  of  service? 

4.  What  steam  rate  may  usually  be  expected  from  simple  single-valve  non-condensing 
engines  at  full  load?     At  fractional  loads? 

5.  What  is  the  most  advisable  cut-off  for  a  simple  non- condensing  single- valve  engine? 
What  is  the  customary  piston  speed? 

6.  What  are  portable  steam  engines?     What  is  their  field  of  service?     In  what  sizes 
are  they  commonly  built? 


SEC.  338]       STEAM  ENGINES  OF  MODERN  TYPES  341 

7.  In  what  sizes  and  forms  are  compound  single-valve  steam  engines  commonly 
manufactured?     What  is  their  field  of  service? 

8.  What  steam  consumptions  may  reasonably  be  expected  of  compound  single-valve 
engines  when  operated  non-condensing?     When  operated  condensing? 

9.  Name  a  well-known  make  of  riding-cut-off  piston-valve  engines.     In  what  sizes  are 
they  manufactured? 

10.  What  forms  of  valves  are  employed  in  four- valve  engines?     What  types  of  gov- 
ernors do  they  employ? 

11.  What  are  the  common  water  rates  of  simple  four-valve  engines  with  Corliss 
valves?     With  poppet  valves? 

12.  What  is  the  principle  of  the  uniflow  engine?     Wherein  does  it  derive  its  great 
economy? 

13.  Name  and  describe  two  ways  in  which  a  uniflow  engine  may  be  constructed  so  as  to 
satisfactorily  operate  non-condensing. 

14.  What  safety  device  is  relied  on  to  automatically  adapt  to  non-condensing  opera- 
tion,   if    the  vacuum  is  destroyed,  uniflow  engines  which  are  designed  primarily   to 
operate  condensing? 

15.  What  are  the  usual  steam  rates  of  condensing  and  non-condensing  uniflow  engines? 
What  exceptional  rate  has  been  reported? 

16.  Are  uniflow  engines  capable  of  carrying  large  overloads?     Why? 

17.  How  does  the  steam  consumption  per  indicated  horse  power  hour  of  a  uniflow 
engine  at  fractional  and  overloads  compare  with  that  at  full  load?     In  this  respect,  how 
does  the  uniflow  engine  compare  with  other  engines? 

18.  What  is  a  locomobile?     With  a  sketch  describe  its  construction.     What  is  its  field 
of  service?     Why?     What  water  rate  may  be  expected  with  this  unit? 

19.  What  are  the  principal  factors  which  will  influence  the  cost  of  a  steam  engine  of 
any  class,  for  a  given  power  output? 

20.  Which  would  you  expect  to  cost  more  per  horse  power,  a  small  engine  or  a  large 
engine?     A  high-speed  engine  or  a  low-speed  engine?     A  high-pressure  engine  or  a  low- 
pressure  engine?     A  condensing  engine  or  a  non-condensing  engine?     An  engine  to  drive 
an  alternating-current  generator  or  one  for  a  mill? 

21.  State  approximate  costs  of  engines  of  the  different  classes. 


DIVISION  12 
STEAM-ENGINE  TESTING 

339.  The  Purposes  Of  Testing  Steam  Engines  are  to  deter- 
mine any  or  all  of  the  following:  (1)  The  operating  conditions. 
(2)   The  mechanical  efficiency.     (3)   The  water  rate.     (4)   The 
thermal   efficiency.     The   purposes   of   the   different  types  of 
tests,  the  apparatus  required,  the  method  of  procedure,  and 
the  calculation  of  the  test  results  are  all  discussed  in  the 
following  sections  of  this  division. 

340.  The  Purpose  Of  An  Operating-Condition  Test  is  to 
ascertain  whether  the  engine  valves  are  functioning  properly 
and  to  determine  mechanical  defects  that  may  exist -within 
the  engine  cylinder.     Tests  of  this  type  involve  only  the  use 
of  steam-engine  indicators  and  correct  interpretations  of  the 
indicator  cards  which  are  obtained  in  the  test  (see  Div.  3 
for  discussion  of  indicators  and  indicator  cards). 

341.  The   Purpose  Of  A  Mechanical -Efficiency  Test   (see 
Div.   10)  is  to  determine  the  energy  lost  in  friction  in  the 
various  bearing  surfaces  of  the  engine.     This  energy  loss  is 
called  the  friction  horse  power.     The  methods  of  conducting 
such  a  test  are  discussed  in  Sees.  368  and  369. 

NOTE. — See  Div.  3  for  discussion  and  rules  for  calculation  of  indicated 
horse  power.  Methods  of  determining  the  brake  horse  power  are  de- 
scribed in  subsequent  sections. 

342.  The  Purpose  Of  A  Water -Rate  Test  is  to  determine 
the  quantity  of  steam,  and  thereby  the  quantity  of  heat,  used 
by  an  engine  per  indicated  or  brake  horse  power.     This  type 
of  test  will  therefore  provide  a  suitable  basis  for  comparing 
one  engine  with  another  with  respect  to  steam  economy. 
The  methods  of  conducting  a  water-rate  test  are  described 
in  Sees.  370  to  373. 

343.  The  Purpose  Of  A  Thermal-Efficiency  Test  is  to  classify 
the  various  heat  losses  of  an  engine  according  to  the  manner 

342 


SEC.  344] 


STEAM-ENGINE  TESTING 


343 


in  which  the  loss  occurs.  Thus,  the  energy  loss  due  to  the  rub- 
bing contact  of  bearings  can  be  found  in  this  type  of  test  and 
classified  as  a  friction  loss.  Also,  as  stated  in  Sec.  318,  the 
thermal  efficiency  of  an  engine  is  a  much  better  measure  of 
its  performance  than  is  its  water  rate,  because  the  water  rate 
depends  upon  operating  conditions.  It  is  therefore  apparent 
that  a  thermal  efficiency  test  is  valuable  to  the  engine  designer 
and  builder  in  that  it  presents  knowledge  essential  to  the 
designing  and  building  of  efficient  engines.  Thermal  effi- 
ciency test  methods  are  considered  in  Sec.  374. 

NOTE. — THE  THERMAL  EFFICIENCY  Is  GENERALLY  CALCULATED  IN 
WATER-RATE  TESTS  and  is  calculated  from  the  results  obtained  in  a 
water-rate  test. 

344.  The  General  Procedure  In  Engine  Testing  consists  of 
operating  the  engine  for  sufficient  time  and  under  suitable 
conditions  to  determine  the  amount  of  (1)  heat  energy  supplied 
to  the  engine  and  the  amount  of  (2)  mechanical  energy  developed 
and  delivered  by  the   engine.     The   determination   of   these 
two  fundamental  quantities  ordinarily  involves  the  collection 
of  data  as  tabulated  below. 

345.  Table  Showing  Data  Necessary  In  An  Engine  Test. 


Quantity  sought 


Data  required 


Heat  input 


Mechanical 
energy 
output 


(a)  Pressure  of  steam  supplied  to  the  engine. 
(6)  Condition     (quality     or    superheat)     of     steam 
supplied  to  the  engine. 

(c)  Weight  of  steam  rejected  by  (or  supplied  to)  the 

engine. 

(d)  Pressure  of  steam  as  it  is  rejected  by  the  engine. 

(e)  Weight  of  the  drip  from  each  jacket. 

(J)1  Temperature  of  the  water  entering  and  leaving 
the  condenser  and  weight  of  circulating  water. 


(a)  Speed  of  the  engine,  in  revolutions  per  minute. 
(6)  Indicator  diagrams  from  each  end  of  each  cylinder, 
(c)  The  engine'slDrake  horse  power  (dynamometer  or 
electric  generator  measurement). 


When  a  heat-balance  (Sec.  12)  is  to  be  made. 


344     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  12 


346.  The  Equipment  Required  For  Engine  Testing  depends 
upon  the  type  of  test  being  made.  In  general,  the  most 
essential  instruments  are:  (1)  Pressure  and  vacuum  gages. 
(2)  Barometers.  (3)  Thermometers.  (4)  Steam  calorimeters. 
(5)  Steam-engine  indicators.  (6)  Planimeters.  (7)  Tachometers 
or  revolution  counters.  (8)  Dynamometers,  or  other  load-meas- 
uring apparatus.  (9)  Steam  condensers  for  condensing  exhaust 
steam.  (10)  Scales  for  weighing  the  condensed  steam.  The 
more  important  of  these  instruments  will  now  be  described. 

NOTE. — Pressure  and  vacuum  gages,  barometers,  thermometers,  and 
steam  calorimeters  are  described  in  the  author's  PRACTICAL  HEAT. 
Indicators  and  planimeters  have  been  discussed  in  Div.  3. 


347.  A  Revolution  Counter  (Figs. 
397  and  399)  is  an  instrument  which 
indicates  the  number  of  revolutions 
made  during  a  period  of  time  by  a 
rotating  shaft  or  wheel.  To  deter- 
mine the  speed  in  revolutions  per 
minute  with  a  revolution  counter,  it 
is  only  necessary  to  divide  the  total 
number  of  revolutions  made  during 
the  period  of  time  by  the  time 
period  expressed  in  minutes. 

Triangular 
Rotating 
'  Disc 


\   ^Revolution 
!     Counter 
^Counter-  Tip 
Inserted  in 
Center  -  Bored 
Hole 


FIG.  397. — Hand  revolution  counter. 


FIG.  398. — Counting  revolutions 
of  an  engine  with  a  revolution 
counter. 


348.  A  Hand  Revolution  Counter  is  shown  in  Fig.  397. 
It  consists  of  a  rotating  disk,  D,  connected  through  worm 
gearing  to  a  short  triangular-pointed  stem,  $,  which  is  pro- 
vided with  detachable  rubber  tips.  In  counting  revolutions 
(Fig.  398),  S  (Fig.  397)  is  inserted  in  the  center-bore  of  the 


SEC.  349]  STEAM-ENGINE  TESTING  345 

crank  shaft  of  the  engine  under  test  and  it  thus  turns  with  the 
shaft  causing  D  to  revolve.  Simultaneously,  the  operator 
looks  at  his  watch  to  keep  an  accurate  account  of  the  time. 
Ordinarily  the  counter  is  permitted  to  run  for  1  min.  The 
operator,  looking  at  the  second  hand  of  his  watch,  inserts  the 
rubber  tip  in  the  center-bore  at  the  start  of  a  minute  and 
removes  it  at  the  end  of  the  minute.  For  each  100  revolutions 
of  S,  D  makes  1  revolution.  In  counting,  the  operator  holds 
his  thumb  over  the  small  stationary  button,  A,  and  " feels" 
each  revolution  of  the  rotating  button,  B,  which  is  attached  to 
D.  The  rubber  tips  are  used  to  prevent  slipping  at  high 
speeds.  This  type  of  revolution  counter  can  be  used  satis- 
factorily for  speeds  up  to  1200  r.p.m. 

349.  A  Continuous  Revolution  Counter  (Fig.  399)  is  gen- 
erally attached  permanently  to  an  engine.     The  operating 
arm,  A,  is  usually  connected  by  a  lever  to  some  engine  part 
having    a    limited    reciprocating    motion.     The    instrument 
is  essentially  a  stroke  counter  constructed  to  add  one  to  the 
dial  reading  for  every  two  strokes 

of  the  engine.  This  type  of  revo- 
lution  counter  may  be  used  satis- 
factorily on  engines  having  speeds 
up  to  250  or  300  r.p.m. 

350.  A   Tachometer    (Figs.  400 
and  401)  is  an  instrument  which 
registers  -the   speed    of   the    shaft 
under  consideration  in  revolutions 
per  minute,  directly  and  at  any  in- 
stant.     Thus,  the  variations  in  its 

indications  from  instant  to  instant  FIG.  399.  —  Continuous  revolution 
will  show  the  different  shaft  speeds 

at  different  instants.  Tachometers  are  most  satisfactory  for 
the  higher  speed  ranges  such  as  those  which  are  attained  in 
steam-turbine  practice,  but  they  may  also  be  used  on  high- 
speed engines.  They  are  manufactured  to  measure  speeds  as 
low  as  20  and  as  high  as  20,000  r.p.m.  However,  because  of 
the  unavoidable  instantaneous  variations  in  the  rotative 
speeds  of  steam  engines,  tachometers  are  entirely  unsuitable 
for  engine-speed  measurements  lower  than,  say,  300  r.p.m. 


346    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.   12 

In  fact,  some  engineers  would  not  use  tachometers  for  measur- 
ing steam-engine  speeds. 

351.  A  Fixed  Tachometer  (Fig.  400)  is  fastened  permanently 
to  some  part  of  the  engine  frame  and  is  belted  from  the  pulley, 
B,  to  the  engine  shaft.     The  mechanism  consists  of  a  spring- 
opposed  centrifugal  governor,  the  movement  of  which  directly 
actuates  the  pointer,  P. 

352.  A  Hand  Tachometer  (Fig.  401)  is  a  governor-operated 
device  internally  geared  to  allow  three  distinct  speed-range 
adjustments.     Adjustment  is  accomplished  by  loosening  the 

TA<-  -Removable 
,  Rubber  Tip 


-Speed  Range 
Space 


Lock  Hut 


-Stand 


FIG.    400. — Fixed    tachometer    (Schaeffer    &  FIG.  401. — Hand  t  ac  h  o  me  t  er. 

Budenburg  Mfg.  Co.)  (Foxboro  Mfg.  Co.) 

locknut,  N,  and  pulling  out  (or  pushing  in)  the  driving  stem, 
S,  until  the  desired  speed  range  is  indicated  in  space  R. 
Then  N  is  tightened.  The  speed  is  indicated  by  the  pointer, 
P,  on  either  the  inner  or  outer  graduated  circles  depending 
upon  the  speed  range  in  use. 

353.  Dynamometers  Or  Load-Measuring  Apparatus  are  of 
extreme  importance  in  engine  testing  and  may  be  divided  into 
two  general  classes:  (1)  Absorption  dynamometers.  (2) 
Electric  generators.  These  are  discussed  separately  in  follow- 
ing sections.  In  acceptance  or  factory  tests  of  engines,  it  is 
usually  necessary  to  so  "load"  the  engine  that  it  will  operate 
at  its  rated-horse-power  output  and  possibly  also  at  other 
outputs  below  and  above  the  rated  output.  The  load-measur- 
ing apparatus  provides  means  whereby  this  loading  can  be 


SEC.  354] 


STEAM-ENGINE  TESTING 


347 


readily  effected  and  measured — whereby  the  engine  can  be 
made  to  do  work  at  a  known  rate. 

354.  Absorption  Dynamometers,   Or  Brakes,   are   of  two 
general  types:  (1)  The  Prony  brake  type  (Figs.  402  to  406), 
wherein  the  power  is  absorbed  by  friction  due  to  a  rubbing 
contact    of    solid    substances.     (2)    The    fluid-friction    type 
(Fig.  409),  wherein  the  power  is  absorbed  by  friction  due  to  the 
turbulence  or  viscosity  of  fluids. 

355.  The  Prony-Brake  Absorption  Dynamometer  (Fig.  402) 
consists  of  a  steel  strap,  S,  bent  to  conform  to  the  shape  of  the 


Wooden  Brake  Arm-^ 


rianged  Hi/wheel 
for  Cooling- 
Wafer 


Steel 
Strap... 


Section  Of  Pulley  Flange- •' 


FIG.  402. — Typical  Prony  brake. 

flywheel  of  the  engine  under  test  and  to  which  wooden  blocks, 
B,  are  fastened  as  shown.  The  steel  strap  is  rigidly  held  at 
one  end,  E,  to  the  brake  arm,  A,  on  one  side  of  the  flywheel  and 
is  fastened  at  its  other  end  to  a  " take-up"  device,  T,  on  the 
other  side  of  the  flywheel.  The  frictional  force  exerted  by  the 
brake  can  be  adjusted  by  means  of  the  hand-wheel  on  the 
" take-up"  device.  A  portable  brake  for  testing  very  small 
machines  is  shown  in  Fig.  403. 

NOTE. — COOLING  OF  THE  PRONY  BRAKE  is  sometimes  essential  to 
prevent  the  wooden  blocks  from  burning  due  to  heat  generated  by  their 
friction  on  the  flywheel  rim.  Effective  cooling  can  be  accomplished  by 
playing  a  small  stream  of  water  upon  the  inside  of  the  flywheel.  Some 
flywheels  and  pulleys  are  flanged  as  shown  in  Figs.  402  and  406;  the  U- 
shaped  space,  U,  Fig.  402,  thus  formed  can  be  filled  with  cooling  water. 
As  the  water  heats  and  evaporates,  it  can  be  replenished. 


348     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.   12 


NOTE.  —  LUBRICATION  OF  THE  PHONY  BRAKE  is  sometimes  necessary 
to  prevent  chattering  and  seizing  of  the  brake  shoes.  Grease  or  heavy 
oil  placed  between  the  brake  blocks  on  the  face  of  the  flywheel  at  its  top 
will  lessen  to  a  great  extent  the  tendency  to  seize  or  chatter. 


f  w/'fh  Heads 

\^"  \  Countersunk  in  the  Wood, 


Hard 

Maple  Blocks •' 


Prony 
Wooden 
Flywheel-Templet 


Brake  Arm  in  Same 
Position  as  For 
Tesf/nq 


FIG.  403. — A  portable  Prony  brake  for  testing  very  small  engines.  (In  testing,  E  is 
pulled  until  the  braking  effect  is  sufficient.  Then  the  D  reading  is  subtracted  from  the 
C  reading.  The  remainder  multiplied  by  the  peripheral  speed  of  A,  in  feet  per  minute, 
gives  the  foot  pounds  per  minute.  This  value  divided  by  "33,000"  gives  the  horse 
power.  E.  E.  Larson  in  Power,  Sept.  13,  1917.) 

356.  The  Use  Of  A  Dynamometer  Of  The  Prony-Brake 
Type  Necessitates  The  Determination  Of  Constants  called 
the  effective  length  of  brake  arm  and  the  tare-weight  of  the  brake. 

The  tare-weight  "Wi"  is  its 
unbalanced  weight  due  to  its 
unsymmetrical  construction. 
This  weight  can  be  found  by  two 
methods:  (1)  Dummy  Flywheel 
Method. — A  wooden  templet,  T 
(Fig.  404),  which  has  the  same 
diameter  as  the  flywheel  of  the 
engine  which  is  to  be  tested,  is 
made.  The  brake  is  then 

tare-weight  of  a  Prony  brake  using  a  mounted  On  this  templet  aS 
wooden  templet  of  flywheel.  (The  shown  and  Supported  On  SaW- 
templet  is  free  to  roll  on  the  pipe  P.)  ,  ~  , 

horses,  St  by  a  shaft  made  of 

pipe,  P,  so  that  the  brake  arm  is  in  the  same  horizontal  position 
as  for  testing.  The  knife-edge  is  supported  on  the  stand,  B. 
Then,  both  the  stand  and  the  brake  are  weighed  on  the  scale,  W. 


Saw -Horse'  '     "'Platform  Scale 

FIG.    404. — Method    of   determining 


SEC.  357]  STEAM-ENGINE  TESTING  349 

This  scale  reading  will  be  the  tare-weight,  "  Wi,"  of  the  brake. 
(2)  Rotation  Method.  —  Arrange  the  brake  as  shown  in  Fig.  402 
and  loosen  the  blocks  on  the  flywheel  until  the  flywheel  turns 
easily.  Turn  the  flywheel  by  hand  in  one  direction  for  one 
or  two  revolutions  and  weigh  the  brake  while  turning  the 
flywheel.  Turning  the  flywheel  in  the  opposite  direction, 
weigh  again.  The  average  of  these  two  weights  (one-half 
their  sum)  will  be  the  tare-weight,  "Wi,"  of  the  brake.  The 
determination  of  the  tare-weight  by  this  method  should  be 
made  two  or  three  times  to  insure  a  fair  average.  Any  stand 
or  pedestal  used  with  the  brake,  for  example,  P,  Fig.  402, 
must  be  weighed  with  the  brake  when  determining  the  tare- 
weight. 

NOTE.  —  THE  EFFECTIVE  LENGTH  OF  THE  BRAKE  ARM,  Lf  (Fig.  402),  is 
the  horizontal  distance,  in  feet,  between  the  vertical  center  line  of  the 
knife-edge  and  the  vertical  center  line  of  the  flywheel  when  the  brake  is  in 
the  working  position. 

357.  When  Using  An  Absorption  Dynamometer,  The 
Brake  Horse  Power  Is  Calculated  By  The  Formula  (its  deriva- 
tion is  given  below)  : 


Wherein:  PbhP  =  brake  horse  power  developed.  Lf  =  effec- 
tive length  of  brake  arm,  in  feet,  as  defined  in  Sec.  356.  N  = 
the  engine  speed,  in  revolutions  per  minute.  W  =  the  gross 
load  on  the  scale,  in  pounds,  as  indicated  by  the  scale  during 
the  test.  Wi  =  the  tare-weight  of  the  brake,  in  pounds,  as 
described  in  Sec.  356.  The  term  (W  -  Wi)  is  frequently 
called  the  net-weight  of  the  brake. 

DERIVATION.  —  Assume  that  the  flywheel  is  held  stationary  on  a  vertical 
axis,  and  that  the  brake  arm  is  pushed  around  the  flywheel  (Fig.  405)  with 
a  force  of  (W  —  Wi)  pounds.  This,  obviously,  is  the  force  which  is 
required  to  rotate  the  brake.  The  distance  through  which  this  force  will 
act  in  one  revolution  =  the  circumference  of  a  circle  of  radius  L/  ft.  = 
2irL/  ft.  Since  N  =  r.p.m.,  the  distance  traveled  in  one  minute  by 
the  friction  sides  of  the  brake  blocks  will  be  ZirL/N  ft.  Hence,  since  the 
force  (W  —  Wi)  acts  through  the  distance  of  2irLfN  ft.  in  one  minute, 
the  work  done  per  minute  will  be  distance  per  minute  X  force  —  2irLfN 
(W  -  Wi)  ft.  Ib.  per  minute.  Now  it  is  evident  that  work  will  be 


350    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  12 

performed  at  the  same  rate  by  the  flywheel  when  it  is  revolving  within  the 
stationary  brake  blocks  as  when  the  brake  blocks  are  revolving  (pushed) 
around  the  stationary  flywheel,  the  speed  being  the  same  in  both  cases. 
Then,  since  by  definition  horse  power  —  foot  pounds  of  work  done  per 
minute  -r-  33,000,  it  follows  that  : 

p 

Pbhp  = 


33,000  -- 

which  is  the  same  as  for  For.  (41). 

EXAMPLE.  —  An  engine  runs  at  a  speed  of  270  r.p.m.  and  its  Prony 
brake  and  stand  push  down  with  a  force  of  250  Ib.  on  a  platform  scale. 
If  the  tare-weight  of  the  brake  is  40  Ib.  and  the  effective  brake-arm 


Work  =Force  x  Distance  =(W-W,)x2TrLfNnLb. 

FIG.  405. — Illustrating  derivation  of  brake  formula.      Work  in  foot  pounds  =  Force  in 
pounds  X   Distance  in  feet  =  (W  -  Wi)  X  2wL/JV. 

length  is  4  ft.  6  in.,  what  brake  horse  power  is  developed  by  the  engine? 
SOLUTION.— Substituting  in  For.  (41):  Pbhp  =  2irLfN(W  -  Wi)/33,000 
=  2  X  3.14  X  4.5  X  270(250  -  40)  -r  33,000  =  48.6  b.h.p.  . 

358.  A  Rope  Brake  Absorption  Dynamometer  (Fig.  406)  is 
a  form  of  the  Prony  brake  in  which  a  rope  is  used  instead  of 
wooden  blocks  to  provide  frictional  resistance.  The  effective 
brake-arm  length  of  a  rope  brake  (L/,  Fig.  407)  is  the  radius 
of  the  flywheel  plus  the  radius  of  the  rope.  Those  portions 
of  the  rope  between  the  flywheel  and  the  rope  ends  must,  in 
a  brake  of  the  type  shown  in  Fig.  406,  be  vertical. 

EXPLANATION. — Considering  the  rope  (Fig.  407)  of  a  rope  brake,  with- 
out the  stand,  the  force  due  to  the  frictional  resistance  of  the  rope  is 


SEC.  358] 


STEAM-ENGINE  TESTING 


351 


transmitted  to  the  scale  as  though  it  were  carried  through  the  center  line 
of  the  rope  end  A  to  the  scale.  Hence  the  effective  brake-arm  length  is 
the  horizontal  distance  from  the  vertical  center  line  of  the  flywheel  to  the 


Rope  Looped 
Through 


Platform  Scale. 


Hanged  Flywheel^ 


Side    View 


Front    View 


FIG.  406. — Typical  rope  brake  on  platform  scale,  S. 


Of 


FIG.  407. — Illustrating  effective  brake- 
arm  of  a  rope  brake. 


Flywheel, 

! 


Effective  Length 
Of  Brake  Arm 


-Hand 
Wheel 


FIG.  408.  —  A  rope  brake.  (The 
effective  brake-arm  length  of  this  brake 
is  measured  between  the  same  points 
as  for  a  Prony  brake.  (See  Fig.  402.) 


center  line  of  the  rope,  or  the  distance  L/.  Fig.  408  shows  a  rope  brake  of 
another  type,  for  which  the  effective  length  of  brake  arm  is  found  in  the 
same  way  as  for  a  wooden-block  Prony  brake. 


352    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  12 


EXAMPLE. — A  rope  brake  (Fig.  406)  made  of  1-in.  rope  is  installed 
on  an  engine  with  a  4-ft.  diameter  brake  wheel.  A  load  of  480  Ib.  is 
balanced  on  a  platform  scale  when  the  engine  is  operating  at  200  r.p.m. 
If  the  tare-weight  of  the  brake  is  80  Ib.,  what  is  the  brake  horse  power 
of  the  engine?  SOLUTION. — The  effective  brake-arm  length,  Lf  = 
(4  +  H2)/2  =  2  +  %4  =  2.0417  ft.  From  For.  (41):  Pbhp  =  2irLfN 
(W  -  W,)/33,000  =  2  X  3,14  X  2.0417  X  200(480  -  80)  -*-  33,000 
=  31.15  h.p. 

359.  The  Water  Brake  Is  A  Dynamometer  Of  The  Fluid- 
Friction  Type  (Fig.  409). — The  principle  of  operation  of  the 
water  brake  is  similar  to  that  of  the  centrifugal  pump.  The 

chief  difference  is  that  the  cen- 
trifugal pump  is  designed  to 
offer  the  least  possible  resist- 
ance to  the  passage  of  water, 
while  the  water  brake  is  designed 
to  offer  the  greatest  possible  re- 
sistance. This  resistance  is  in- 
troduced by  cupping  the  casing 
and  constricting  the  water- 
outlet  areas.  The  rotor  (im- 
peller) of  the  water  brake  is 
coupled  to  and  rotates  with  the 
shaft  of  the  engine  under  test. 
The  stationary  part  is  equiva- 
lent to  the  brake  arm  of  a  Prony 
brake. 


To  59 


FIG.  409. — Illustrating  principle  of  the 
water  brake. 


EXPLANATION. — Water  is  admitted  to  the  impeller  chamber,  C, 
through  the  hollow  shaft,  S.  This  water  is  then,  by  centrifugal  force, 
forced  out  radially  through  the  holes  in  the  impeller  to  the  spaces,  R, 
between  the  impeller  arms.  As  these  arms  rotate,  the  water  is  thrown 
into  the  cups,  D,  in  the  stationary  casing  wherein  eddy  currents  are 
formed.  These  eddy  currents  oppose  the  rotation  of  the  impeller  and 
thereby  cause  the  knife-edge  to  press  down  on  the  scale.  The  water 
eventually  finds  its  way  through  the  small  clearances  between  the  impeller 
and  casing  to  the  water  outlet.  The  water  pressure  in  the  brake  can  be 
adjusted  to  meet  various  load  conditions  by  throttling  the  valves  on  the 
water  inlet  and  outlet  pipes.  The  greater  the  pressure  within  the  casing, 
the  greater  the  load  which  it  imposes  on  the  scale. 

NOTE. — THE  BRAKE  HORSE  POWER  ABSORBED  BY  A  WATER  BRAKE 
is  found  by  For.  (41).  The  effective  brake-arm  length  (Lf)  Fig.  409)  is 


SEC.  360] 


STEAM-ENGINE  TESTING 


353 


found  as  with  a  Prony  brake.     The  tare-weight  of  this  brake  is  found  by 
Method  2  in  Sec.  356. 

360.  Electrical  Loading  Of  An  Engine  (Fig.  410)  is  accom- 
plished by  coupling  or  belting  an  engine  to  an  electric  generator 
of  known  efficiency  (Sec.  362)  and  measuring  the  power  output 
of  the  generator.  The  generator  is  connected  to  a  variable 
electrical  load — usually  a  water  rheostat — whereby  the  power 
required  of  the  engine  to  drive  the  generator  can  be  varied 
at  the  will  of  the  operator.  Either  an  alternating-current 
(A.C.)  or  a  direct-current  (D.C.)  generator  may  be  used. 


Mechanical  Load  Delivered  By 


Electrical  Energy  Dissipated  As  Heat-^ 

Electrical  Power  Measuring  • *~ 

Instrumentfltattmeterl 


Engine  Under/  Mechanical  Load 
Test          "  Generator  By  Belt-/ 


Of97K.W. 


FIG.  410. — Illustrating  principle  of  electrical  loading  of  an  engine  (Engine,  E,  is 
pulling  147  mechanical  h.p.  Of  this,  the  electrical  load  on  generator,  G,  which  is  indicated 
on  P,  and  which  is  dissipated  in  water  rheostat,  R,  comprises  97  kw.  or  130  h.p.) 


NOTE. — WHEN  GENERATORS  ARE  BELTED  To  ENGINES  ALLOWANCE 
MUST  BE  MADE  FOR  SLIPPAGE  OF  THE  BELT.  This  allowance  can  be 
made  by  the  following  formula,  the  derivation  of  which  is  given  below. 

(4V  P  N"  di"p  fhn^ 

v***/  -toAp  —    »T/   7  /  -*np  ^n.p. ) 

1\     di 

Wherein:  P&/,p  =  brake  horse  power  of  engine.  N"  =  speed  of  engine 
in  revolutions  per  minute,  di"  =  diameter  of  engine  pulley,  in  inches. 
N'  =  speed  of  generator  pulley,  in  revolutions  per  minute,  di'  =  diam- 
eter of  generator  pulley,  in  inches.  PhP  =  horse  power  input  to  generator 
(Sec.  362). 

DERIVATION. — The  horse  power  transmitted  by  a  belt  =  (the  net  belt 
pull — the  force  transmitted — in  pounds)  X  (the  distance,  in  feet,  through 
which  the  force  acts  in  one  minute)  +  33,000.  That  is,  1  h.p.  =  33,000 
ft.  Ib.  per  min.  The  distance  through  which  the  net  belt  pull  acts  in  one 
minute  is  the  circumference,  in  feet,  of  the  pulley  over  which  it  runs 
times  the  number  of  revolutions  it  makes  in  one  minute.  That  is, 
if  the  pulley  diameter  is  expressed  in  inches,  the  distance  =  N"  X  IT 
X  di"  I  12.  Hence  the  horse  power  transmitted  to  a  belt  by  its  engine 
pulley  can  be  expressed  by  the  formula: 


(44) 


bhp 


Netbeltpull  XN"  Xir  X  di"/(l2  X  33,000)  (h.p.) 


23 


354    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  12 
Transforming  this  equation  for  the  engine  pulley,  it  becomes: 


(45)  Net  bell  pvll  =  12  X  Ob.) 


If  For.  (44)  represents  the  brake  horse  power  given  to  the  belt  by  the 
engine  which  drives  the  belt,  similarly  the  net  horse  power  given  to  the 
generator  by  the  belt  can  be  represented  by  : 

(46)  Php  =  Net  belt  pull  X  N'  X  *  X  di'/(12  X  33,000)  (h.p.) 
From  which  it  follows  that,  for  the  generator  pulley  : 

j*.\  -m  r       i     1         t  i  77  J-  ^       -^N      OO.UUv/       /\      XflW  /n  v 

(47)  Net  belt  pull  =  -  ^-r—  —  (Ib.) 

irN  di 

Since  the  net  belt  pull  at  the  engine  is  the  same  as,  and  equal  to,  the 
net  belt  pull  at  the  generator,  Fors.  (45)  and  (47)  may  be  equated,  thus: 


(48)     Net  belt  pull  -  12  X  ^OMX  ^  =  ^^j™,  *  ^        Ob.) 

or  transposing  and  dividing  by  12  X  33,000  and  multiplying  by  TT 

N"d  •" 
(49;  PbhP  =  -5757^*1.  (h.p.) 

Which  is  the  same  as  For.  (43). 

EXAMPLE.  —  A  generator  having  a  2-ft.  diameter  pulley  was  driven  by  a 
belt  from  an  engine  having  a  6-ft.  diameter  flywheel.  If  the  speed  of 
the  engine  was  200  r.p.m.  at  90  h.p.  input  to  the  generator  and  the  speed 
of  the  generator  was  585  r.p.m.  at  this  load,  what  was  the  brake  horse 
power  of  the  engine?  SOLUTION.  —  From  For.  (43):  PbhP  -  (N"di" 
/N'di'^Php  =  [(200  X  72)  -r-  (585  X  24)]  X  90  =  92.4  b.h.p. 

361.  To  Determine  The  Electrical  Output  Of  A  Direct- 
Current  Generator  (Fig.  411)  the  procedure  is  as  follows: 

A  voltmeter,  E,  to  measure  the 
-Ammeter  difference    in    electric   potential 

(e.m.f.)  between  the  leads,  is 
connected  in  parallel  with  the 
load;  see  Sec.  365  for  "  Water 
Rheostat."  An  ammeter,  7, 
to  measure  the  current  flowing 
through  the  leads,  is  inserted 

generator,  GD.     Using  ammeter,  /,  and     in     SCI'ieS    with     the    load.       The 

voltmeter,  E.  ammeter  and  the  voltmeter  are 

read  at  the  same  instant.  The  power  output  of  the  generator 
in  kilowatts  is  then  found  by  substituting  the  observed  values 
in  the  following  formula: 

El 

(50)  Pkw  =  (kw.) 


SEC.  362] 


STEAM-ENGINE  TESTING 


355 


Wherein:  Pkw  =  the  power-output  of  the  generator,  in  kilo- 
watts. E  =  the  voltage  or  e.m.f.,  in  volts,  as  indicated  by  the 
voltmeter.  I  =  the  current,  in 
amperes,  as  read  from  the 
ammeter  at  the  same  instant 
the  voltmeter  is  read. 


-  ^'--'Jo  Load      Direct- Current  Genercrf-or< 


NOTE. — A  DIRECT-CURRENT  WATT- 
METER MAY  BE  USED    (P,  Figs.  410 


Fia.  412.  —  Illustrating  load-output 


and  412)  instead  of  a  voltmeter  and  determination  with  a  direct-current 
an  ammeter.  It  is  connected  as  shown  generator,  GD,  using  a  direct-current 
and  reads  directly  the  product  El  wattmeter,  P.  (Note.— Single-phase 
(For  ^0}  alternating-current  generator  load  de- 

terminations   may  be    made   as  illus- 
trated  if  an  alternating-current  wattmeter 
362.    TO    Find    The  Horse-     is  used  instead  of  a  direct-current  watt- 

Power  Input  To  Any  Generator    meter  as  shown.) 

When  Its  Power  Output  Is  Known   (1   h.p.  =  0.746  kw.) 

substitute  in  the  formula: 


Or   since,    for   direct-current   generators',    For.    (50)  :   Pkw  = 
#7/1000,  it  is  true  for  direct-current  generators  that: 

WT 
(52)  P.,  =  (h.p.) 


Wherein:  Php  =  the  horse-power  input  to  the  generator- 
Ed  =  the  efficiency  of  the  generator  at  the  developed  load, 
expressed  decimally. 

NOTE.  —  THE  EFFICIENCY  OF  A  GENERATOR  AT  ANY  LOAD  CAN  BE 
READ  FROM  ITS  EFFICIENCY  GRAPH.  This  graph  is  usually  plotted 
between  per  cent,  load  and  per  cent,  efficiency  or  between  amperes  load  at 
rated  voltage  and  per  cent,  efficiency.  The  graph  can  be  obtained  from  the 
manufacturer  of  the  generator  by  giving  the  serial  number  and  all  other 
name-plate  data  relating  to  the  machine. 

EXAMPLE.  —  A  steam  engine  is  coupled  to  and  driving  a  direct-current 
generator,  Gd,  Fig.  411.  If  the  voltmeter,  E,  reads  220  volts,  the  ammeter 
7,  764  amp.,  and  the  efficiency  of  the  generator  at  this  load,  as  shown  by 
its  efficiency  graph,  is  0.90,  what  is  the  horse-power  input  of  the  engine  to 
the  generator?  SOLUTION.—  By  For.  (52)  :  Php  =  EI/74QEd  =  220 
X  764  H-  (746  X  0.90)  =  250  h.p. 

363.  To  Determine  The  Electrical  Load  With  A  Single- 
Phase,  Or  Two-Phase,  Alternating-Current  Generator  (Figs. 
413  and  414)  use  an  alternating-current  wattmeter,  P,  in  each 


356    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  12 

phase  which  will  read  Pfcu,  directly  for  that  phase.  The  total 
output  of  a  two-phase  generator  is  always  the  sum  of  the 
wattmeter  readings  for  each  of  the  two  phases.  The  horse- 
power input  is  found  by  For.  (51).  For  a  single-phase  alter- 
nating-current circuit  an  alternating-current  wattmeter  may 
be  connected  in  the  same  way  (Fig.  412)  as  is  a  wattmeter  on  a 
two-wire  direct-current  circuit. 


iloact 


.-  Alternating  Current 
Wattmeter 

Two -Or  Three-Phctse 

Alternating  Current 

Generator. 


Alternating  Current 
Wattmeter 

2-Phcrse, 

Alternating  Current 


FIG.    413. — Method    of    determining  FIG.    414. — Method    of    determining 

power  output  of  a  3-wire,  2-phase  alter-  power    output    of    a    4-wire,    2-phase, 

nating-current  generator,  G.     (Note. — •  alternating-current  generator,  GA. 
The  power    of  a  3-wire  3  phase,  alter- 
nating-current  generator    may  also  be 
determined  as  illustrated  above.) 

NOTE. — IN  A  THREE-WIRE  TWO-PHASE  SYSTEM  always  be  sure  that 
the  connections  are  made  as  shown  in  Fig.  413;  that  is,  with  a  wattmeter 
current  coil  in  each  of  two  lead  wires  and  the  voltage  coils  of  each  watt- 
meter connected  to  the  common  return  wire. 

EXAMPLE. — If  wattmeter  PI  (Fig.  413)  reads  30  kw.  and  wattmeter  P2 
reads  35  kw.,  what  is  the  horse-power  input  of  the  engine  to  the  generator, 
if  the  generator  efficiency  at  this  load  is  0.88? 

SOLUTION. — The  total  power  output  of  the  generator  in  kilowatts, 
Pfcu>  =  the  sum  of  the  wattmeter  readings  =  PI  +  P%  =  30  +  35  =  65  kw. 
The  horse  power  input  to  the  generator  from  For.  (51)  is:  P/ip  = 
PAu,  /0.746Ed  =  65  -i-  (0.746  X  0.88)  =  96  h.p. 

364.  To  Determine  The  Electrical  Load  With  A  Three  - 
Phase  Alternating-Current  Generator  (Fig.  413)  two  alter- 
nating-current wattmeters,  PI,  and  P^  are  connected  in  any 
two  of  the  three  phases.  The  sum  of  the  readings  of  the  two 
wattmeters  will  be  the  total  output,  Pkw,  of  the  generator. 
To  determine  the  horse-power  input  to  the  generator  substitute 
in  For.  (51). 


SEC.  365]  STEAM-ENGINE  TESTING  357 

NOTE. — IN  USING  Two  WATTMETERS  IN  A  THREE- W  IRE,  THREE-PHASE 
ALTERNATING-CURRENT  CIRCUIT  neither  of  the  meters  measures  the  power 
in  any  one  of  the  three  phases.  With  light  loading  one  of  the  meters  will 
probably  give  a  negative  reading,  and  it  is  necessary  to  reverse  either  its 
current  or  potential  leads  in  order  that  the  deflection  may  be  noted.  In 
such  cases,  the  algebraic  sums  must  be  taken  and  not  the  numerical 
sums.  In  other  words,  if  one  reads  +  500  watts  and  the  other  —  300 
watts,  the  total  power  in  the  circuit  will  be :  500  —  300  =  200  watts. 

As  the  load  comes  on,  the  readings  of  the  instrument  which  gave  a 
negative  deflection  will  decrease  until  they  drop  to  zero,  and  it  will  then 
be  necessary  to  again  reverse  the  potential  leads  on  this  wattmeter. 
Thereafter,  the  readings  of  both  instruments  will  be  positive,  and  the 
numerical  sum  of  the  two  will  be  the  power  consumption  of  the  load. 

365.  Where  No  Useful  Load  Is  Available,  Generator 
Loading  May  Be  Accomplished  Satisfactorily  By  A  Water 
Rheostat  (Fig.  415). — Where  the  power  developed  by  the 
generator,  which  furnishes  the  load,  can  be  conveniently 
employed  for  a  "useful  load"  as  for  electric  lighting  or  heating 
or  for  motor-driving  other  machinery  it  should,  obviously,  not 
be  wasted.  In  many  plants  the  power  developed  by  the  test 
generator  can  be  fed  into  the  main  bus,  thus  relieving  the 
other  regular  generators  of  part  of  their  load.  But  where 
such  procedure  is  not  feasible,  it  is  usual 
to  employ  a  water  rheostat  as  the  most 
convenient  means  of  dissipating  the  test- 
load  power. 


EXPLANATION. — The  water  rheostat  shown  in 
Fig.  415  consists  of  two  iron  electrodes,  P  and  S, 
one  supported  from  a  rope,  R,  which  passes  over  a 
pulley.  The  other  rests  upon  the  bottom  of  the 
barrel.  The  barrel  is  filled  with  water,  W.  Each  ^Genemtor\  Wooden  Barret 

Leads          Iron  flectrocfe 

electrode  is  connected  to  a  generator  lead.      The  _,      . ,  _     w  , 

..  .  FIG.  415. — Water  rheostat 

distance  between  electrodes  may  be  adjusted  to        for  2-wire  systems. 
vary  the  resistance  offered  by  the  water  to  the 

passage  of  current.  Hence  the  distance  between  electrodes  determines 
the  load  on  the  generator.  For  voltages  below  1000  volts  it  is  usually 
necessary  to  add  salt  to  the  rheostat  water  to  decrease  its  resistance 
sufficiently  that  a  great  enough  current  will  flow. 

366.  In  Determining  The  Water  Rate  Of  Steam  Engines,  A 
Steam  Condenser  Is  Often  Employed  (Fig.  416). — As  shown, 
the  steam  after  being  used  by  the  engine  is  exhausted  through 


358    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  12 

the  exhaust  pipe,  E,  into  the  condenser,  C,  where  it  is  con- 
densed. The  condensate  (condensed  steam)  runs  out  through 
the  condensate  pipe.  0}  into  the  weighing  tank,  T.  In  T  it  is 
weighed  on  the  scale,  S.  The  procedure  when  using  a  steam 
condenser  is  taken  up  in  following  sections.  For  descriptions 
of  condensers  see  the  author's  STEAM  POWER  PLANT  AUX- 
ILIARIES AND  ACCESSORIES. 

,-5team  Pressure  Ga&e 
Steam 
-Valve 


Pooling  Water 

'Cooliriy  Water  Inlet 
Water  Seal-- 
Tank Ft 


FIG.  416. — Illustrating  apparatus  used  in  water-rate  test. 

367.  The  Detailed  Procedure  In  Testing  An  Engine  Is 
usually  about  as  indicated  in  the  paragraphs  which  follow: 

1.  Specifically  decide  the  object  of  the  test  and  keep  this  in  mind, 
not  only  during  the  performance  of  the  test,  but  also  during  the  prepara- 
tion of  the  equipment  for  conducting  the  test. 

2.  Precautions    should  be   taken  to  insure  that  the  engine  and  its 
lubricating  system  are  in  condition  for  continuous  running  for  at  least 
the  period  of  the  test  without  danger  of  a  shut-down  for  adjustments  or 
repairs.     Any  interruption   of   operation   during   the   test  period   will 
probably  decrease  the  reliability  of  the  test. 

3.  The    name   plate,  and  other  data  pertaining  to  the  engine  itself 
and  to  the  equipment  and  instruments  used,  should  be  recorded  on  the 
log  sheet. 

4.  All  test   instruments   such  as  gages,  thermometers,  tachometers, 
scales,  indicators,  reducing  motions,  etc.,  should  be  carefully  examined 
and,  in  tests  where  the  greatest  accuracy  is  desired,  should  be  calibrated 
before  and  after  the  test  (allowances  should  be  made  in  the  test  data  for 
any  discrepancies  in  calibration  or  otherwise  that  may  exist).     Great 


SEC.  368]  STEAM-ENGINE  TESTING  359 

care  should  be  used  in  attaching  test  instruments  to  the  engine  as  inac- 
curate readings  can  be  obtained  from  the  most  accurate  instruments 
when  incorrectly  installed. 

5.  The  engine  should  run  under  test  conditions  for  a  sufficient  length 
of  time  to  allow  all  conditions,  such  as  temperatures,  pressures,  etc.,  to 
become  constant  before  data  readings  are  taken.     This  is  necessary  in 
order  that  true  test  conditions  be  attained  prior  to  recording  test  data. 

6.  The  first  set  of  readings  may  be  taken  after  conditions  have  become 
constant.     The  time  and  all  necessary   data  should  be  immediately 
recorded  on  a  data  sheet  previously  arranged.     All  readings  thereafter 
should  be  taken  at  equal  time  intervals  throughout  the  test.     The 
necessary  time  interval  will  depend  on  the  duration  of  the  test  and  the 
constancy  of  the  load  (see  Sec.  375). 

7.  After  the  test  has  been  completed  the  test  apparatus  should  be 
carefully  cleaned  and  indicators  should  be  oiled  to  prevent  rusting. 

8.  Computations  for  test  results  should  then  be  made  and  checked  for 
accuracy.     See  following  sections  for  methods  and  formulas  used  in 
calculating  the  test  results. 

9.  Finally,  graphs  should  be  plotted  on  ruled  or  squared  paper  to 
visualize  the  test  results.     In  mechanical  efficiency  tests  there  should  be 
plotted   such  graphs   as   "mechanical  efficiency"   against   "brake   horse 
power,"    "speed"    against   "brake   horse   power,"    and   "indicated  horse 
power"    against   "brake  horse   power."     In  the   water-rate  tests   there 
should  be  plotted  such  graphs  as  "total  pounds  of  steam  consumed  per 
hour"  against  "indicated  horse  power"  "water  rate"   against  "indicated 
horse    power,"    "boiler    pressure"    against  "time,"   "exhaust  pressure" 
against  "time,"  and  "thermal  efficiency"  against  "indicated  horse  power." 

368.  In  Testing  A  Simple  Engine  To  Determine  Its  Mechan- 
ical Efficiency,  it  is  merely  necessary  to  ascertain:  (1)  Its 
brake  horse  power  output  with  a  dynamometer  or  electric  generator; 
Sees.  353  to  365.  (2)  Its  indicated  horse  power  with  steam 
engine  indicators;  see  Div.  3.  Then,  as  explained  in  Div.  10, 
the  brake  horse  power  (output)  divided  by  the  indicated  horse 
power  will  be  the  mechanical  efficiency.  The  apparatus  is 
arranged  as  shown  in  Fig.  417.  It  is  usually  desirable  to 
ascertain  the  brake  and  the  indicated  horse  power  at  a  number 
of  different  loads  so  that  the  efficiencies  at  these  different 
loads  may  be  determined.  Usually  the  final  data  are  plotted 
into  a  graph:  Mechanical  Efficiency  against  Load. 

NOTE. — IT  Is  USUALLY  ADVANTAGEOUS  To  INCREASE  OR  DECREASE 
THE  BRAKE  HORSE  POWER  LOAD  ON  THE  ENGINE  IN  EQUAL  STEPS  when 
mechanical  efficiency  tests  are  being  made.  The  values  of  brake  horse 
power  which  are  usually  taken  are  >£,  J£,  Y±,  1,  and  1^  of  the  full-load 


360    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div,  12 


rating  of  the  engine.  This  loading  permits  the  plotting  of  a  well-pro- 
portioned mechanical-efficiency  graph.  A  minimum  of  three  indicator 
diagrams  should  be  taken  from  each  end  of  the  cylinder  for  each  load  in 
order  that  an  average  mean  effective  pressure  (Sec.  122)  may  be  obtained 
for  each  load. 

NOTE. — IMMEDIATELY    AFTER    DIAGRAMS    ARE    TAKEN,    INDICATOR 
CARDS  SHOULD  BE  MARKED  with  a  symbol  designating:  (1)  From  which 


Platform 
5ca/e-, 
/ 


Prony 

Brake- 
Me  fa/  Brake 


Steam  Supply  P/'pe---^ 
Steam  Supply  Pressure  Gaae^ 
Reducing 

Continuous  I 
Engine  Under  \  Revolution 


l>l 


Exhaust  Pressure  Gage-1' 
FIG.  417. — Arrangement  of  apparatus  for  a  mechanical-efficiency  test  on  a  simple  engine. 


end  of  the  cylinder  they  were  taken.  (2)  The  speed  of  the  engine.  (3)  The 
brake  load  when  taking  the  card.  (4)  The  time  at  which  the  card  was  taken. 
This  is  necessary  to  forestall  errors  when  computing  the  test  results. 

369.  Data  Which  Should  Be  Recorded  On  The  Data 
Sheet  In  A  Mechanical-Efficiency  Test  are:  (1)  Time. 
(2)  Brake  load.  (3)  Speed.  (4)  Steam  pressure.  (5)  Exhaust 

pressure.  These  data 
should  be  shown  on  the 
data  sheet.  (Fig.  418) 
even  if  some  of  them  du- 
plicate data  shown  on  the 
indicator  cards.  An  accu- 
rate record  of  the  steam 


Test 
No. 

Time 

Speed 

Load  on 

ftSS 

Remarks 

FIG.  418. — Data    (log)    sheet   for   mechanical- 
efficiency  engine  test. 


and  exhaust  pressures,  as  indicated  by  pressure  gages,  Gs  and 
GE,  Fig.  417,  is  usually  necessary  because  the  engine  perform- 
ance is  directly  affected  by  these  pressures. 

370.  In  Testing  A  Simple  Engine  To  Determine  Its  Water 
Rate,  it  is  merely  necessary  to  ascertain :  (1)  Its  indicated  horse 
power  with  steam  engine  indicators  (Div.  3).  (2)  Its  brake 


SEC.  870] 


STEAM-ENGINE  TESTING 


361 


Wafer  Supply    Valve  E 
Pipe~±       Closed-., 


horse  power  with  a  dynamometer  or  electric  generator,  Sees. 
353  to  365.  (3)  The  rate  at  which  it  uses  steam — by  condensing 
the  steam  or  by  measuring  the  boiler-feed  water  for  a  suitable 
time  period.  (4)  The  condition  (quality  or  superheat)  of 
its  supply  steam  with  a  steam  calorimeter  or  a  steam  ther- 
mometer. Then,  since  the  water  rate  of  an  engine  is  usually 
expressed  as  the  number  of  pounds  of  dry  steam  it  uses  per 
indicated  (or  brake)  horse  power  per  hour,  the  water  rate  can 
be  readily  computed.  It  is  customary  to  find  the  water  rate  of 
engines  at  different  engine  loads 
(Sec.  368)  and  then  to  plot  the 
results  into  a  graph:  Water  Rate 
against  Load. 

EXPLANATION. — Fig.  416  shows  the 
arrangement  of  equipment  for  a  water- 
rate  test.  A  steam  condenser,  C,  is  used 
in  this  case  for  condensing  the  exhaust 
steam  from  the  engine  in  order  that  the 
condensed  steam  may  be  weighed  to  de- 
termine the  water  rate  of  the  engine.  A 
steam-pressure  gage,  G,  and  a  steam 
calorimeter,  Q,  should  be  placed  on  the 
steam-supply  pipe,  H,  so  that  the  quality 
(Sec.  371)  of  the  steam  which  is  used  by 
the  engine  may  be  determined.  Sim- 
ilarly, a  pressure  gage,  B,  should  be 
placed  between  the  engine  and  the  con- 
denser to  determine  the  back  pressure  in 
the  exhaust  pipe,  E. 

NOTE. — IN  SMALL  PLANTS  IT  Is  OFTEN 
CONVENIENT  To  WEIGH,  OR  METER,  THE 
FEED  WATER  To  THE  BOILER  WHICH 
SUPPLIES  STEAM  To  THE  ENGINE  UNDER 
TEST  (Fig.  419)  for  the  determination 
of  its  water  rate  instead  of  weighing  the 
steam  after  it  has  passed  through  the 
engine  as  is  shown  in  Fig.  416.  When 
the  boiler-feed  method  is  used,  care  should  be  taken  to  insure  that  the 
boiler  water  level  and  the  boiler  steam  pressure  are  the  same  at  the  finish 
of  the  test  as  they  were  at  its  start. 

NOTE. — IF  THE  SUPPLY  STEAM  Is  SUPERHEATED,  a  thermometer  should 
be  located  in  the  steam-supply  pipe  adjacent  to  the  throttle  valve  in  addi- 
tion to  the  equipment  shown  in  Fig.  416.  This  thermometer  will  indicate 


Suction  Line  To  Bo!/er  feed  Pump—'"' 
FIG.  419. — Equipment  arrange- 
ment for  weighing  boiler  feed- 
water.  (Two  weighing  tanks,  A 
and  B,  are  mounted  on  platform 
scales  above  a  suction  tank,  C,  from 
which  water  is  supplied  to  the 
boiler-feed  pump.  By  means  of 
the  valve  arrangement  shown,  one 
tank,  A,  can  be  filled  with  water 
and  weighed  while  the  other  tank, 
B,  discharges  its  water  into  the 
suction  tank,  C.  The  water  level 
in  tank,  C,  should  be  at  the  same 
height  at  the  end  of  the  test  as  it 
was  at  the  beginning  of  the  test.) 


362     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  12 

the  temperature  of  the  supply  steam.  A  knowledge  of  this  temperature 
is  necessary  to  determine  the  amount  of  superheat  (see  Sec.  426)  of  the 
steam. 

371.  Data  Which  Should  Be  Recorded  On  The  Data  Sheet 
In  A  Water -Rate  Test  are  the  same  as  for  a  mechanical- 
efficiency  test  with  the  addition  of:  (1)  The  temperature  of 
the  steam  in  the  steam  calorimeter,  if  the  supply  steam  is  wet. 

(2)  The  temperature  of  the  supply  steam,  if  it  is  superheated. 

(3)  The  weights  of  steam  used  by  the  engine  for  each  load,  as 
the  load  is  usually  applied  in  increments  as  explained  in 
Sec.   368.     The  quality  and  pressure  of  the  supply  steam 
(or  the  temperature  of  the  supply  steam,  if  superheated)  and 
the  pressure  of  the  exhaust  steam  are  important  in  water- 
rate  tests  as  the  steam  consumption  of  engines  is  directly 
affected  by  these  quantities. 

NOTE. — STEAM  QUALITY  AND  ITS  DETERMINATION  are  discussed  in 
the  author's  PRACTICAL  HEAT.  To  find  the  quality  of  steam  with  a 
throttling  calorimeter  substitute  in  the  following  formula,  the  derivation 
of  which  is  given  in  PRACTICAL  HEAT: 

100[gd2  +  Cm(T/2  -  TV,)  -  Hi] 

(53,  xp  =  -  (per  cent.) 

nv 

Wherein :  xp  =  the  quality  of  the  steam  in  the  engine  supply  pipe,  in  per 
cent.  Hdz  =  the  total  heat  of  dry  saturated  steam  at  the  pressure  existing 
in  the  calorimeter,  in  British  thermal  units  per  pound.  Tf2  =  the 
temperature  in  the  calorimeter,  in  degrees  Fahrenheit.  T/3  =  the 
temperature  of  saturated  steam  at  the  pressure,  which  is  usually  assumed 
to  be  the  barometric  pressure,  existing  in  the  calorimeter,  in  degrees 
Fahrenheit.  HI  =  the  heat  of  the  liquid  at  the  pressure  existing  in  the 
engine  supply  pipe,  in  British  thermal  units  per  pound.  Hv  =  the 
latent  heat  of  steam  at  the  pressure  existing  in  the  steam  supply  pipe,  in 
British  thermal  units  per  pound.  Cm  =  the  mean  specific  heat  of 
superheated  steam,  in  British  thermal  units  per  pound  per  degree  Fahren- 
heit rise  in  temperature,  and  which  may  be  considered  as  equal  to  0.46. 

All  of  the  above  properties  of  steam  can  be  found  in  any  standard 
steam  table. 

CAUTION. — All  steam  tables  are  arranged  for  absolute  pressures  and 
not  for  the  gage  pressures  as  indicated  by  gages.  To  obtain  the  absolute 
pressure  in  any  case,  it  is  only  necessary  to  add  the  atmospheric  pressure 
(Barometric  pressure),  expressed  in  pounds  per  square  inch,  to  the 
pressure  indicated  by  the  gage.  See  author's  PRACTICAL  HEAT  for  an 
explanation  of  this  situation. 


SEC.  372]  STEAM-ENGINE  TESTING  363 

EXAMPLE.  —  In  Fig.  420,  if  the  barometric  pressure  is  14.7  Ib.  per  sq  in., 
the  temperature  of  the  steam  in  the  throttling  calorimeter  270  deg.  fahr., 
and  the  steam  pressure  is  150  Ib.  gage  (164.7  Ib.  abs.),  what  is  the 
quality  of  the  steam  supplied  to  the  engine?  SOLUTION.  —  Substituting 
in  For.  (53)  : 

xp    =    100[ffd2    +    Cm(Tfi    -  TVs)       •    Hi\/Hv    = 

100[1150.4  +  0.46(270  -  212)  -  338]  +  856.8  =  98  per  cent. 
The  per  cent,  of  moisture  in  the  steam  =  100  —  98  =  2  per  cent. 

372.  In  A  Water-Rate  Test,  It  Is  Necessary  To  Express 
The  Weight  Of  Wet  Steam  Used  By  An  Engine  In  Terms  Of 
Weight  Of  Dry  Steam  Used  as  all  water  rates  are  expressed 
in  pounds  of  dry  steam  per  indicated  —  or  brake  —  horse  power 
per  hour.     If  the  engine  being  tested  is  taking  wet  steam 
(steam  of  less  than  100  per  cent,  quality),  the  weight  of  dry 
steam  used  can  be  found  by  substituting  in  the  formula: 

(54)  Wsd  =  xdWsw  (Ib.    of   dry   steam) 

Wherein:  Wsd  =  the  weight  of  dry  steam  used,  in  pounds. 
xd  =  the  quality  of  the  steam,  expressed  decimally.  Wsw  = 
the  weight  of  wet  steam  used. 

373.  The  Water  Rate  Of  An  Engine  Can  Be  Calculated 
by  the  following  formula  if  the  water  rate  is  to  be  based  on 
indicated  horse  power: 

(55)  Wsdi  =  5  —  ^—  (Ib.  dry  steam  per  i.h.p.  hr.) 


or  if  the  water  rate  is  to  be  based  on  brake  horse  power: 
(56)  Wsdb  =  ~  —  s~^r  (Ib.  dry  steam  per  b.h.p.  hr.) 

A  bhp/\th 

Wherein:  Wsdi  =  the  water  rate  based  on  indicated  horse 
power,  in  pounds  of  dry  steam  per  indicated  horse  power  per 
hour.  Wadb  =  the  water  rate  base  on  brake  horse  power, 
in  pounds  of  dry  steam  per  brake  horse  power  per  hour. 
Wkd  =  the  total  weight,  in  pounds,  of  dry  steam  consumed 
during  the  time  th,  in  hours.  P^P  =  the  average  indicated 
horse  power  developed  during  the  time  period  th.  PbhP  = 
the  average  brake  horse  power  developed  during  the  time 
period  4. 

EXAMPLE.  —  In  Fig.  420  if  the  engine  develops  85  i.h.p.  and  2550  Ib. 
ofsteam  are  used  per  hour,  what  is  the  water  rate  of  the  engine  in  pounds 


364     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  12 

of  dry  steam  per  indicated  horse  power  per  hour?  SOLUTION. — In  the 
example  under  Sec.  371,  it  was  found  that  the  quality  of  the  steam  was  98 
per  cent,  or  0.98.  From  For.  (54),  the  total  weight  of  dry  steam  used 
=  Wsd  =  xdWsw  =  0.98  X  2550  =  2499  Jh.  From  For.  (55),  the  water 
rate=  Wsdi  =  Wsd/PaP  Xth  =  2449  +  (85  X  1)  =  29.4  Ib.  of  dry  steam 
per  i.h.p.  hr. 

NOTE. — THE  WATER  RATE  OF  AN  ENGINE  CAN  BE  CALCULATED 
APPROXIMATELY  BY  MEANS  OF  INDICATOR  CARDS  (see  Div.  3).  This 
method  is  often  used  to  check  other  methods  of  determining  the  water 
rate. 


Engine  Header  Supplying  2550  Lb.  Of  Steam 
<-—3-Phase,  /L~C  Circuit               Calorimeter  Thermometer--.  . 
A-C.  Wattmeter  Tf2  =™T. '^ 


Exhaust  Pressure  4  Lb.  Per  Sq.  In-' 


FIG.  420.  —  Illustrating  calculation  of  water  rate  and  thermal  efficiency  of  engine,  M, 

using  generator,  G. 


374.  To  Determine  The  Thermal  Efficiency  Of  An  Engine, 
it  is  necessary  to  know:  (1)  The  rate  at  which  work  is  done  by 
an  engine  (its  power  output).  (2)  The  rate  at  which  heat  is 
furnished  to  the  engine  (its  power  input.)  Both  of  these  are 
reduced  to  British  thermal  units  per  hour  per  horse  power. 
Then,  as  explained  in  Div.  10,  if  the  value  for  (1)  is  divided 
by  that  for  (2)  the  thermal  efficiency  will  be  the  result.  The 
power  output  is  found  by  measuring  the  indicated  horse  power 
(Div.  3).  Sometimes,  brake  horse  power  is  considered  as  the 
power  output.  The  brake  horse  power  is  measured  with  a 
dynamometer  or  electric  generator  (Sees.  353  to  365).  The 
power  input  is  found  by  ascertaining  the  water  rate  of  the 
engine  and  the  heat  consumed  per  pound  of  steam  used 
(Div.  10).  Hence  it  is  obvious  that  the  values  necessary  for 
the  computation  of  the  thermal  efficiency  are  obtained  from 
1  the  same  test  data  as  are  required  in  a  water-rate  test  (Sees. 
370  to  373). 


SEC.  375]  STEAM-ENGINE  TESTING  365 

NOTE. — THE  THERMAL  EFFICIENCY  CAN  ALSO  BE  CALCULATED  BY 
FOLLOWING  THE  TEST  CODE  OF  THE  AMERICAN  SOCIETY  OF  MECHANICAL 
ENGINEERS  which  is  given  in  a  condensed  form  in  Sec.  381.  The  TEST 
CODE  is  a  conveniently  arranged  form  consisting  of  the  logical  and 
successive  steps  to  be  taken  in  the  calculation  of  engine-test  results. 

EXAMPLE. — If  the  back  pressure  (exhaust  pressure)  in  Fig.  420  is  4  Ib. 
gage  (18.7  Ib.  abs.),  what  is  the  thermal  efficiency  of  the  engine 
based  on  indicated  horse  power?  SOLUTION. — By  For.  (32)  in  Sec.  317, 
Htl  =xdHv  +  Hi.  By  For.  (31):  Edti  =  2545/W.i(#»  -  Hit). 
Now,  from  Fig.  420:  Wsi  =  2550  -=-  85  =  30  Ib.  peri.h.p.  hr.  Therefore, 
with  the  results  found  in  the  example  under  Sec.  371  and  taking  values 
from  a  standard  steam  table,  the  thermal  efficiency  =  Ed«  =  2545/ 
Wai[(xdHv  +  Hi)  -  Hi,}  =  2545  -J-  30[(0.98  X  856.8  +  338)  -  192.6] 
=  0.0854  =  8.54  per  cent.  =  thermal  efficiency  based  on  indicated  horse 
power. 

EXAMPLE. — If  the  supply  steam  in  the  preceding  example  were 
superheated  instead  of  wet  and  if  the  temperature  of  the  steam  at  the 
throttle  was  435.4  deg.  fahr.,  what  would  be  the  thermal  efficiency  of  the 
engine  based  on  indicated  horse  power?  SOLUTION. — From  For.  (31), 
the  thermal  efficiency  =  Edti  =  2545/Wsi(#,  -  Hi2)  =  2545  -5-  [30 
(1,235.9  -  192.6)]  =  2545  +  31,299  =  0.0814  =  8.14  per  cent.  =  ther- 
mal efficiency  based  on  indicated  horse  power. 

375.  The  Duration  Of  A  Test  Depends  Upon  The  Type  Of 
Test  Being  Made. — For  a  mechanical-efficiency  test,  sufficient 
time  should  be  allowed  for  five  or  six  load  increments  to  be 
applied.     For  water-rate  tests  the  TEST  CODE  of  the  American 
Society  of  Mechanical  Engineers  specifies : 

"A  test  for  steam  or  heat  consumption,  with  substantially  constant 
load,  should  be  continued  for  such  time  as  may  be  necessary  to  obtain  a 
number  of  successive  hourly  readings,  during  which  the  results  are 
reasonably  uniform.  For  a  test  involving  the  measurement  of  feed- 
water  for  this  purpose,  five  hours  duration  is  sufficient.  Where  a  surface 
condenser  is  used,  and  the  measurement  is  that  of  the  water  discharged 
.  .  . ,  the  duration  may  be  somewhat  shorter.  In  this  case  successive 
half-hourly  records  may  be  compared  and  the  time  correspondingly 
reduced.  When  the  load  varies  widely  at  different  times  of  the  day,  the 
duration  should  be  such  as  to  cover  the  entire  period  of  variation." 

376.  An  Acceptance  Test  Is  A  Water -Rate  Test  on  a  new 

engine  conducted  under  the  observation  of  both  the  purchaser 
and  the  seller  to  determine  whether  the  economy,  or  pounds 
of  steam  per  indicated  horse  power  hour  (or  brake  horse  power 
hour),  for  different  loads  is  as  economical  as  was  specified  in 
the  purchasing  contract  (see  Sec.  456). 


366    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  12 

377.  In  Testing  Compound  Engines  the  same  procedure  can 
be  followed  as  described  in  Sec.  367.  In  such  a  test,  indicator 
cards  must  be  taken  from  both  the  high-  and  low-pressure 
cylinders  (see  Div.  8).  The  total  indicated  horse  power 
of  the  engine  will  be  the  sum  of  the  indicated  horse  power  of 
the  high-  and  of  the  low-pressure  cylinders.  The  temperature 
and  pressure  of  the  steam  in  the  receiver  should  be  recorded 
with  the  other  data.  An  arrangement  of  apparatus  for  testing 
a  compound  engine  is  shown  in  Fig.  421. 


Supply       Jhermome-ter 

Steam,      ;'    Steam  Calorimeter 

/  /  ,'Tandem-Compound Engine  Under  Test       fan?       flandwheel 
*•  •'  '   -Indicators        .Continuous     ^^^^Brake.  ( Adjustment 


Platform 


5upp/u  tfeamror  Humps      'Condensate  Line 


Condensate 
Tank--. 
Condenser 

Platform 
Scale  for 
Weighing  \ 


Circulating 
Htofer/n/et 


Steam 
Cylinder 


FIG.  421. — Arrangement  of  equipment  for  determining  the  water  rate  of  a  tandem- 
compound  engine.  (Horse  power  is  measured  with  brake  B.  Steam  used  by  engine,  E, 
is  condensed  in  C  and  the  condensate  weighed  in  W.) 

378.  In  Testing  High-Speed  Engines  care  should  be  used  to 
determine  the  speed  accurately.     The  indicators  and  reducing 
motion  should  be  examined  for  lost  motion  as  this  may  cause 
a  noticeable  deformation  of  the  indicator  cards.     Some  simple 
method  (see  the  note  under  Sec.  101)  should  be  provided  for 
connecting  and  disconnecting  the  indicator  cord  from  the 
reducing  motion,  as  this  is  often  difficult  to  do  on  high-speed 
engines.     The  brake  load  should  be  applied  carefully  as  a 
slight  inaccuracy  in  loading  may  cause  a  large  error  in  power. 

379.  The  Clearance  Volume  Is  Often  Determined  In  Engine 
Testing  especially  to  enable  the  plotting  of  the  theoretical 


SEC.  379] 


STEAM-ENGINE  TESTING 


367 


-Bucket 


expansion  curve  (Sec.  108).  The  clearance  volume  may  be 
found  by  setting  the  engine  carefully  on  dead  center  (Sec.  153) 
and  filling  the  clearance  volume  with  water  from  a  previously 
weighed  container.  The  difference  in  weight  of  the  container 
before  and  after  filling  the  clearance  space  will  give  the  weight 
of  the  water  in  the  clearance 
space.  From  this,  the  volume 
of  water  in,  or  the  volume  of, 
the  clearance  space  may  be 
calculated. 

NOTE. — ALLOWANCE  SHOULD  BE 
MADE  FOR  LEAKY  PISTONS  AND 
VALVES  WHEN  THE  CLEARANCE  Is 
BEING  DETERMINED  by  this  method. 
Data  may  be  obtained  (Fig.  422)  for 
the  necessary  correction  in  this  way: 
(1)  Observe  the  time  and  quantity  of  \  \  ^ater  Leaking  Past  Piston 

\  \       "Piston  at  End  of  Stroke 

water  required  to  fill  the  clearance  space      \        Clearance  Space  Filled  with  Water 

at  a  uniform  rate.     (2)  Note  the  quan-        "Outlet  to  indicator  cock 

tity  of  water  required  to  keep  the  clear-   FlG-  422.— Method  of  determining  clear- 


ance  space  completely  filled  for  any  con- 


ance  volume  in  an  engine  cylinder- 


venient   length   of  time.      (3)  The  clearance  volume  may  then  be  found  by 
substituting  in  the  following  formula: 


(57) 


(cu.  in.) 


Wherein:  Vi  =  the  clearance  volume,  in  cubic  inches.  Vn  =  the 
volume  of  water,  in  cubic  inches,  originally  necessary  to  fill  the  clearance 
space  at  a  uniform  rate,  tt\  =  the  time,  in  seconds,  originally  required  to 
fill  the  clearance  space  with  the  quantity  of  water  V%\.  Vii  =  the  volume 
of  water,  in  cubic  inches,  necessary  to  keep  the  clearance  space  com- 
pletely filled.  tsi  =  the  time,  in  seconds,  required  for  introducing  the 
volume  of  water  Ft-2. 

DERIVATION.  —  If  no  leakage  occurred,  Vi,  the  clearance  volume,  in 
cubic  inches,  would  be  equal  to  F»i,  which  is  the  volume  of  water,  in 
cubic  inches,  originally  necessary  to  fill  the  clearance  space  at  a  uniform 
rate.  But  if  there  is  leakage,  then  the  volume  of  water  lost  through 
leakage  must  be  determined.  It  is  apparent  that  during  the  time  tsi, 
which  elapses  while  the  clearance  space  is  filled  with  F»i,  the  rate  of 
leakage  around  the  piston  begins  at  zero  and  finally  attains  a  maximum 
as  the  water  level  reaches  the  top  of  and  fills  the  clearance  space.  It 
follows  that  the  average  rate  of  leakage  during  the  tsi  seconds  is  (very 
nearly)  one-half  of  the  maximum  rate.  This  maximum  rate  is  found  after 
the  clearance  volume  is  full  by  introducing  Viz.  The  maximum  rate  is 


368    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  12 

Viz  -5-  tS2.  The  average  rate  during  t»\  is  therefore  one-half  the  maximum 
=  Ft-2/2£s2.  The  time  required  to  introduce  Vu  was  t»i.  Therefore: 
since  total  leakage  during  the  time  =  the  rate  X  the  time,  it  follows  that, 

(58)  leakage  =  ~  X  tsl  (cu.  in.) 

^1*2 

which  must  be  subtracted  from  Vi  i  to  find  the  net  volume  of  the  clearance 
space,  Vi.  Therefore,  by  subtraction: 


(59) 

which  is  the  same  as  For.  (57). 

EXAMPLE.  —  If  it  takes  120  sec.  to  fill  the  clearance  space  of  an  engine 
having  a  leaky  piston  with  30  cu.  in.  of  water,  and  it  takes  10  cu.  in.  of 
water  to  keep  the  clearance  space  completely  filled  for  200  sec.,  what  is 
the  true  clearance  volume?  SOLUTION.  —  By  For.  (57):  the  true  clearance 
volume  =  Vi  =  Vu  -  tsiVi2/2tsZ  =  30  -  [(120  X  10)  -r-  (2  X  200)] 
=  30  -  [1200  -5-  400]  =  30  -  3  =  27  cu.  in. 

380.  It  Sometimes  Facilitates  The  Computation  Of  Test 
Results  If  The  Engine  And  Brake  Constants  Are  Calculated. 

These  constants  are  the  numerical  results  of  certain  factors 
which  will  occur  in  test  computations  several  times  and  if  the 
constants  are  calculated  at  the  start  of  the  test  computations, 
some  time  will  be  saved.  The  engine  constants  are  obtained 
from  For.  (13)  of  Sec.  121  and  will  not  be  discussed  here. 
The  brake  constant  is  obtained  from  For.  (41),  Sec.  357, 
which  is 


(60)  ft,,  -  (b.h.p.) 


Wherein:  2:  TT:  33,000;  and  L/  (effective  length  of  brake  arm 
in  feet)  are  all  constant  values  for  each  test.  The  brake 
constant  then  is: 

(61)  kb  =  00  ^^  (brake  constant) 

oo,UUU 

The  brake  horse  power  formula,  For.  (41),  then  becomes: 

(62)  Pbhp  =  kb  N(W  -  Wi)  (b.h.p.) 

Wherein:  PbhP  =  the  brake  horse  power  developed.  kb  =  the 
brake  constant.  N  =  the  speed  of  the  engine,  in  revolutions 
per  minute.  W  =  the  gross  load  on  the  scale,  in  pounds. 
Wi  =  the  tare-  weight  of  the  brake,  in  pounds,  as  explained 
in  Sec.  356. 


SEC.  381]  STEAM-ENGINE  TESTING  369 

EXAMPLE. — If  the  effective  brake-arm  length  for  an  engine  is  5  ft., 
what  is  the  brake  constant?  SOLUTION. — From  For.  (61)  the  brake 
constant  =  kb  =  27rL//33,000  =  (2  X  3.14  X  5)  +  33,000  =  0.000,953 
=  the  brake  constant. 

EXAMPLE. — If,  for  the  above  engine,  a  600-lb.  load  is  indicated  by  the 
platform  scale,  the  tare-weight  of  the  brake  is  50  lb.,  and  the  speed  of  the 
engine  is  180  r.p.m.,  what  brake  horse  power  is  developed  by  the  engine? 
SOLUTION. — From  For.  (62),  the  brake  horse  power  =  Pbhp  =  kbN 
(W  -  Wi)  =  0.000,953  X  180(600  -  50)  =  94.3  b.h.p. 

381.  An  Outline  Of  The  American  Society  Of  Mechanical 
Engineers,  Steam -Engine  Test  Code  which  will  standardize 
procedure  and  will  promote  accuracy  and  rapidity  of  calcula- 
tion follows: 

DATA  AND  RESULTS  OF  STEAM-ENGINE  TESTS 
CODE  OF  1915 


1.  Test  of engine  located  at. 

To  determine 

Test  conducted  by 


DIMENSIONS,  ETC. 

2.  Type  of  engine . . . .  : 

3.  Rated  power  of  engine , 

(a)  Name  of  builders 

(6)  Kind  of  valves 

(c)  Type  of  governor 

4.  Diameter  of  cylinder in. 

5.  Stroke  of  piston ft. 

DATE  AND  DURATION 

6.  Date 

7.  Duration hr. 

AVERAGE  PRESSURES  AND  TEMPERATURES 

8.  Pressure  in  steam  pipe  near  throttle,  by  gage lb.  per  sq.  in. 

9.  Barometric  pressure in.  of  mercury. 

(a)  Pressure  at  boiler,  by  gage lb.  per  sq.  in. 

10.  Pressure  in  receiver,  by  gage lb.  per  sq.  in. 

11.  Pressure  in  exhaust  pipe  near  engine,  by  gage lb.  per  sq.  in. 

12.  Temperature  of  steam  near  throttle .deg. 

13.  Temperature  of  steam  in  exhaust  pipe  near  engine deg. 

QUALITY  OF  STEAM 

14.  Percentage  of  moisture  in  steam  near  throttle  or  number  of  degrees 

of  superheat per  cent,  or  deg. 

14 


370    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  12 

TOTAL  QUANTITIES 

15.  Total  water  fed  to  boiler Ib. 

16.  Total  condensed  steam  from  surface  condenser  (corrected  for  con- 

denser leakage) Ib. 

17.  Total  dry  steam  consumed  (Item  15  or  16  less  moisture  in  steam).  .Ib. 

HOURLY  QUANTITIES 

18.  Total  water  fed  to  boilers  or  drawn  from  surface  condenser  per 

hour Ib. 

19.  Total  dry  steam  consumed  for  all  purposes  per  hour  (Item  17  -r-  Item 

7) Ib. 

20.  Dry  steam  consumed  per  hour  for  all  purposes    foreign    to    the 

main  engine Ib. 

21.  Dry  steam  consumed  by  engine  per  hour  (Item  19  —  Item  20) Ib. 

HOURLY  HEAT  DATA 

22.  Heat  units  consumed  per  hour  [Item  21  X  (total  heat  of  steam  per 

pound  at  pressure  of  Item  8  minus  heat  in  1  Ib.  of  water  at  tem- 
perature of  Item  13)] B.t.u. 

INDICATOR  DIAGRAMS 

23.  Commercial  cut-off  in  per  cent,  of  stroke per  cent. 

24.  Initial  pressure  above  atmosphere Ib.  per  sq.  in. 

25.  Back  pressure  at  lowest  point  above  or  below  atmosphere 

Ib.  per  sq.  in. 
SPEED 

26.  Revolutions  per  minute r.p.m. 

(a)  Variation  of  speed  between  no  load  and  full  load per  cent. 

POWER 

27.  Indicated  horse  power  developed i.h.p. 

28.  Brake  horse  power b.h.p. 

29.  Friction  of  engine  (Item  27  —  Item  28) h.p. 

ECONOMY  RESULTS 

30.  Dry  steam  consumed  by  engine  per  i.h.p.  hr Ib. 

31.  Dry  steam  consumed  by  engine  per  b.h.p.  hr Ib. 

32.  Heat    units    consumed  by  engine  per  i.h.p.  hr.    (Item  22  -f-  Item 

27) B.t.u. 

33.  Heat   units   consumed  by  engine  per  b.h.p.  hr.    (Item  22  -r-  Item 

28) B.t.u. 

EFFICIENCY  RESULTS 

34.  Thermal  efficiency  of  engine  referred  to  i.h.p.  (2546.5  -5-  Item  32) 

X  100 per  cent. 

35.  Thermal  efficiency  of  engine  referred  to  b.h.p.  (2546.5  -r-  Item  33) 

X  100 per  cent, 

SAMPLE  DIAGRAMS 

36.  Sample  diagrams  from  each  cylinder 


SEC.  381]  STEAM-ENGINE  TESTING  371 

"NOTE. — For  an  engine  driving  an  electric  generator  the  form  should 
be  enlarged  to  include  the  electrical  data,  embracing  the  average  voltage, 
number  of  amperes  in  each  phase,  number  of  watts,  number  of  watt 
hours,  average  power  factor,  etc.  and  the  economy  results  based  on  the 
electric  output  embracing  the  heat  units  and  steam  consumed  per 
electric  h.p.  hr.  and  per  kw.  hr.  together  with  the  efficiency  of  the 
generator." 

EDITOR'S  NOTE. — THE  THERMAL  EFFICIENCY  As  FOUND  IN  THE 
ABOVE  TEST  CODE  WILL  DIFFER  BY  A  SMALL  PERCENTAGE  FROM  THE 
THERMAL  EFFICIENCY  As  FOUND  BY  For.  (31),  Sec.  317.  This  is  due  to 
the  fact  that  in  Item  22  of  the  above  code  the  total  heat  units  consumed 
by  an  engine  is  considered  as:  XaW»i(Bti  —  Hit),  while  from  Fors.  (31) 
and  (32),  the  total  heat  consumed  by  an  engine  =  WSi(xdHv  +  HI) 
—  Hiz.  Wherein:  Ws»  =  the  weight  of  wet  steam  consumed  by  the 
engine  per  indicated  horse  power  hour.  xd  =  the  quality  of  the  supply 
steam  expressed  decimally.  Hti  =  the  total  heat  in  1  Ib.  of  steam 
at  the  supply  pressure,  in  B.t.u.  Hiz  =  the  heat  in  1  Ib.  of  water 
at  exhaust  pressure,  in  B.t.u.  HI  =  the  heat  in  1  Ib.  of  water  at  the 
supply  pressure,  in  B.t.u.  Hv  =  the  latent  heat  of  vaporization  of 
1  Ib.  of  steam  at  the  supply  pressure,  in  B.t.u.  The  difference  in  thermal 
efficiencies,  as  found  by  these  two  different  methods,  will  generally  not 
amount  to  more  than  one-half  of  1  per  cent. 

QUESTIONS  ON  DIVISION  12 

1.  What  are  the  purposes  of  testing  steam  engines? 

2.  What  is  meant  by  the  term  brake  horse  power? 

3.  What  is  meant  by  the  term  total  indicated  horse  power? 

4.  What  is  meant  by  the  term  friction  horse  power? 

5.  What  is  the  mechanical  efficiency  of  an  engine? 

6.  What  is  the  difference  between  a  revolution  counter  and  a  tachometer? 

7.  What  are  the  two  general  classes  of  load-measuring  apparatus? 

8.  What  is  a  Prony  brake?     Draw  a  sketch  and  describe  one. 

9.  What  is  the  principle  of  operation  of  a  fluid-friction-type  brake? 

10.  What   is   meant  by  the  term  effective  length  of  brake  arm?     Illustrate  with  a 
sketch. 

11.  What  is  the  effective  length  of  brake  arm  for  a  rope  brake? 

12.  What  is  the  tare-weight  of  a  brake  and  how  is  it  determined? 

13.  How  may  the  electrical  loading  of  engines  for  testing  be  accomplished? 

14.  How    is    the    power    output    of    a    three-phase    alternating-current    generator 
determined? 

15.  Illustrate  with  a  sketch  how  the  wattmeter  connections  should  be  made  for 
determining  the  power  output  of  a  three-phase,  three- wire,  alternating-current  generator. 

16.  What  is  the  water  rate  of  a  steam  engine? 

17.  How  are  steam  engine  water  rates  usually  expressed? 

18.  What  apparatus  is  necessary  in  a  water-rate  test?     Draw  a  sketch  and  explain. 

19.  When  and  how  is  the  steam  calorimeter  used  in  engine  testing? 

20.  What  is  the  general  procedure  in  testing  an  engine? 

21.  How  should  the  load  be  applied  in  engine  testing? 

22.  What  data  are  necessary  in  a  water-rate  test  of  a  compound  engine? 

23.  What  precautions  are  necessary  in  testing  high-speed  engines? 

24.  How  may  the  clearance  volume  of  an  engine  be  determined? 


372    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  12 

PROBLEMS  ON  DIVISION  12 

1.  An  engine  develops  120  brake  horse  power  on  an  indicated  horse  power  of  133 
What  is  the  mechanical  efficiency?    What  is  the  friction  horse  power? 

2.  What  is  the  brake  horse  power  developed  by  an  engine  (Fig.  423)  at  a  speed  of 
220  r.p.m.  with  a  net  weight  of  250  Ib.  on  the  platform  scale,  if  the  effective  length  of  the 
brake  arm  is  63  in.? 

3.  What  is  the  brake  constant  for  a  iH-in.  rope  brake  (Fig.  424)  on  a  6-ft.  diameter 
flywheel? 

4.  An  engine  uses  5000  Ib.  of  steam  (97  per  cent,  quality)  per  hour  when  developing 
200  h.p.  (indicated).     What  is  the  water  rate  of  the  engine  in  pounds  of  dry  steam  per 
indicated  horse  power  per  hour? 


Effective  Brake  Arm  Length.^ 

( 63-- . -V—; 

t,-Prony  Brake 


Flywhee,. 
6 Ft  Diameter, 


4  Diameter 
X  Rope 


flywheel  Speed  =  220  r.p.m. 

FIG.  423. — What  is  the  brake  horse 
power? 


FIG. 


424.—  What    is    the 

stant? 


brake    con- 


5. The  engine  of  Fig.  420  uses  2550  Ib.  of  steam  per. hour.     What  is  its  water  rate  in 
pounds  of  dry  steam  per  brake  horse  power  per  hour,  if  the  wattmeters  read  20.2  kw.  and 
30.7  kw.  as  illustrated  and  the  generator  efficiency  at  this  load  is  90  per  cent.?     What  is 
the  thermal  efficiency  based  on  brake  horse  power? 

6.  A  certain  engine  develops  a  total  indicated  horse  power  of  200  with  steam  pressure 
at  200  Ib.  per  sq.  in.  gage  and  exhaust  pressure  at  8  Ib.  per  sq.  in.  gage.     If  the  quality  of 
the  supply  steam  is  99  per  cent,  and  the  mechanical  efficiency  of  the  engine  is  90  per 
cent,  at  this  load,  what  is  the  thermal  efficiency  of  the  engine  based  on  brake  horse 
power  when  the  steam  consumption  is  42,000  Ib.  in  a  10-hr 'shift?     (Assume  barometric 
pressure  is  14.7  Ib.  per  sq.  in.). 


DIVISION  13 

RECIPROCATING-ENGINE     MANAGEMENT,     OPERA- 
TION AND  REPAIR 

382.  The  Purposes   Of  Proper  Engine  Management  are: 
(1)    Reliability.     (2)    Efficiency.     Reliability   is   secured   by 
anticipating  all  common  sources  of  trouble,  such  as  knocks, 
hot  bearings,  clogged  condenser  passages  and  all  accidents  by 
careful    attention    while    the    engine    is    running;   and  post- 
poning the  repairs,  adjustment  and  overhauling  which  will 
eventually  be   necessary  until   a  shut-down   is   convenient. 
A  definite  upper  limit  which  the  efficiency  of  an  engine  cannot 
exceed  is  fixed  by  its  design;  but  the  efficiency  may  be  pre- 
vented  from   becoming   unduly   low   by  avoiding  excessive 
leakage  and  friction,  and  by  correct  adjustment.     A  skillful 
operator  can,  by  the  sound,  detect  most  troubles  in  an  engine 
room  with  which  he  is  familiar.     By  early  detecting  and 
correcting  trouble  and  by  regular  inspection,  an  engine  may 
be  kept  in  perfect  condition  with  a  minimum  of  effort. 

383.  An  Important  Duty  Of  An  Engineer  Is  To  Become 
Thoroughly  Familiar  With  The  Equipment  Which  He  Is  To 
Operate. — The  first  day  which  an  engineer  spends  in  a  new 
plant  or  one  for  which  he  is  to  assume  responsibility  usually 
provides    the    best    opportunity    for    a    general    inspection. 
Among  the  parts  which  it  is  well  to  include  in  such  an  inspec- 
tion are: 

1.  Cylinders.  If  the  cylinder  heads  have  been  removed  (or  if  there 
is  time  for  removing  them)  see  that  the  piston-rod  nuts  and  bolts  of  the 
follower-plate,  F  (Fig.  425),  are  tight  and  well  secured.  A  set  screw  or 
lock  nut  (Fig.  426)  is  recommended  for  the  piston-rod  nuts.  Note  the 
condition  of  the  cylinder  walls,  whether  they  are  scored  or  pitted.  Note 
also  the  linear  clearance  between  the  piston  and  cylinder  head  at  the 
end  of  the  stroke,  and  mark  this  distance  on  the  guides  for  reference. 
While  the  cylinder  head  is  off,  the  amount  of  piston  and  valve  leakage 

373 


374    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE   [Div.  13 


may  be  noted  by  admitting  a  little  steam  to  the  crank  end  at  crank-end 

dead  center  and  noting  the  escape  of  steam.     Use  a  good  gasket  coated 

with  graphite  in  closing  the  cjdinder.     In 

replacing  the  cylinder  head,  be  sure  that 

the  cylinder  walls  are  free  from  grit,  are 

well  lubricated,  and  that  no  tools  or  other 

obstructions  remain  in  the  cylinder. 

2.   Valves.     If   valve  chest  covers  are 
off    (or   if   there   is   time   for   removing 


SetScrew 
•Flush  Nut 

,   ,  —       _       _      _«  Counferbored 
I-  Flush  Nut  With  Set  Screw'     Piston 
'it  Pin. 


Set  Screw 


\  -  Longitudinal 
Section 


H-End   Partial- 
Sectional  Elevation 


FIG.  425. — Piston  construction  used  in  the 
St.  Louis  Corliss  engine.  A  taper  cotter,  K,  is 
used  in  place  of  the  usual  piston-rod  nut.  (St. 
Louis  Iron  and  MachineWorks). 


Common  Nut  With  Set  Screw 


FIG.    426.  —  Showing     methods    of 
locking  piston-rod  nuts. 


Waste 


Clamping 
Bolt-* 


them)  note  the  condition  of  the  valves.     Measure  the  laps  (Sec.  143) 
for  future   adjustment  and  if  feasible  make  templets  as  described  in 

Sec.  157.  Also  note  the  valve  action  by 
turning  the  engine  over  by  hand  (if  the 
engine  is  small)  with  the  cover  off.  Make 
sure,  in  replacing  the  covers,  that  the  valve 
chest  is  clean,  the  rubbing  surfaces  well 
lubricated,  and  that  the  gaskets  used  for 
the  covers  are  in  good  condition.  Pump 
valves,  if  found  in  poor  condition,  should  be 
refaced  or  replaced. 

3.  Flywheel.  Note  if  the  dead  centers  are 
marked  (Sec.  153)  on  the  flywheel  rim  for 
valve  setting.  If  the  engine  is  small,  turn 
it  over  by  hand  to  see  if  there  is  undue  fric- 
tion in  its  bearings. 


FIG.  427. — Simple  split  bearing. 


4.  Bearings.  Any  bearings  or  boxes  which  are  dissembled  should 
be  examined,  cleaned  if  necessary  and  adjusted.  The  condition  of  all 
bearings  and  their  oil  passages  should  be  ascertained  as  far  as  possible. 


SEC.  383]    RECIPROCATING-ENGINE  MANAGEMENT 


375 


Clean  out  oil  holes,  put  in  fresh  oil  and  fill  with  waste  (Fig.  427)  if 
exposed. 

5.  Stuffing  boxes.     If  the  packing  appears  to  be  in  good  condition,  oil  it 
and  screw  up  to  a  reasonable  compression.     If  not,  repack  (Sec.  415). 

6.  Auxiliaries.     The  engineer  is  usually  in  charge  of  some  or  all  of 
the  power  plant  auxiliaries.     For  care  of  these,  see  the  author's  STEAM 
POWER  PLANT  AUXILIARIES  AND  ACCESSORIES. 


Bach  Pressure  \hlve 


To 
Heating  Sys  tern- 

.'Steam 
Separator 

,  Throttle 
••'     Valve 


Feed-Water  Heater 
Ana"  Receiver-:, 

'Steam  Trap- 


Feed-Pump  Exhaust''  "'  Boiler- feed  Pump 

FIG.  428. — Auxiliary  piping  and  equipment  used  in  connection  with  non-condensing 

steam  engine. 

7.  Pumps.     These  should  be  given  the  same  sort  of  inspection  as 
the  engine  as  far  as  it  is  applicable;  see  STEAM  POWER  PLANT  AUXILIARIES 
AND  ACCESSORIES. 

8.  Condensers.     If   the   steam-space   manhole   cover   or  water-space 
cover  of  a  surface  condenser  is  removed,  note  the  condition  of  the  tubes 
inside  and  out.     If  the  grease  is  excessive  on  the  outside,  the  steam  space 
should  be  filled  with  water  and  boiled  out.     The  water  in  the  steam 
space  will  issue  from  any  split  tubes  or  leaky  tube  glands.     These  should 
be  renewed,  repacked  or  tightened  as  required.     The  condition  of  the 
sprays  and  passages  of  a  jet  condenser  should  be  ascertained  if  possible. 
See  the  author's  STEAM  POWER  PLANT  AUXILIARIES  AND  ACCESSORIES 
for  further  information  relating  to  condenser  operation  and  maintenance. 


376    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE   [Div.  13 


9.  Piping.     Trace  out  all  piping  connected  with  the  engine  (Figs. 
428  and  441)  and  the  auxiliaries.     If  difficulty  is  experienced  in  keeping 

the  piping  in  mind,  sketch  diagrams 
(Fig.  429)  may  be  used,  or  instead 
the  different  systems,  i.e.,  city  water, 
low-pressure  steam,  condenser  water, 
etc.,  may  be  marked  with  occasional 
stripes  of  different  colors.  The  loca- 
tions of  all  valves  should  be  care- 
fully noted.  Piping  that  is  rusting 
rapidly  should  be  cleaned,  painted 
and  protected  from  water  if  possible. 
Exposed  steam  or  hot-water  piping 
should  be  lagged.  Exhaust  lines  to 
condensers  (Fig.  430)  and  atmosphere 
and  valves,  G,  for  changing  from 
condensing  to  non-condensing  oper- 
ation should  be  examined. 

10.  Drains.  Drains  both  on  the 
engine  and  piping  and  the  traps 
used  in  connection  with  them  should 

rIG.  429.-Sketch  diagram  of  piping.       be   noted   and   tegted   to   make  gure 

that  they  are  clear. 

11.  Instruments.     The  pet  cocks  on  gage  glasses  should  be  tested 
to  see  if  they  are  clear.     It  should  be  noted  whether  the  pressure  gages 


Condenser        Cooling- Wafer 
Cone -..  Supply-. 

Relief  Va/ve  ---  = ' ' 


Vacuum 
/Condensing  Engines*         Gages-, ^- 


Exhaust  Cuf-Out  Valves" 


'Exhaust-  Sfecrm 
Header 


FIG.  430. — Showing  how  several  engines,  E,  may  be  operated  condensing    with  one 
barometric  condenser. 

and  thermometers  work  properly.     If  time  permits,   they  should  be 
tested  or  calibrated. 


SEC.  384]  RECIPROCATING-ENGINE  MANAGEMENT 


377 


12.  Tools.     See  that  tools  for  oiling  and  for  simple  repairs  and  adjust- 
ments are  in  place. 

13.  Supplies.     See  that  cylinder  and  engine  oil  and  grease,   gasket 
stock,  piston  and  candle-wicking  packing,  waste,  red  lead,  graphite,  and 
other  supplies  are  on  hand. 

384.  All  Steam  Engines  Should  Be  Warmed  And  Drained 
Before  Starting.— The  pipe,  A  (Fig.  431),  leading  to  the  engine 
should  be  warmed  and  drained  before  the  throttle,  C,  is  given 
a  large  opening.  This  is  to  insure  that  the  steam  which  con- 
denses in  warming  the  pipe  will  not  run  into  the  engine.  To 


/Stop  Valve 


Cylinder  Drain  Pipe  «  .    ED 
Drain  Line  To  Live-  Steam  Trap— 


FIG.  431.  —  ;Steam  piping  for  a  simple  engine. 

do  this,  the  drain  valve,  D,  should  be  opened  and  stop  valve, 
B,  opened  a  very  little.  While  the  pipe,  A,  is  being  warmed, 
the  drain  valves,  E  and  F,  should  be  opened  and  the  throttle, 
(7,  loosened  on  its  seat  to  prevent  sticking.  After  the  pipe,  A, 
is  warmed,  the  valve,  B,  may  be  opened  wide;  but  neither  B 
nor  C  should  be  opened  suddenly  since  a  sudden  large  flow  of 
steam  through  a  pipe  is  likely  to  draw  water  from  the  boiler 
which  may  wreck  the  piping.  Then  either  the  throttle,  C, 
or  by-pass  valve,  G,  may  be  opened  slightly  to  warm  up  the 
engine. 

NOTE.  —  LARGE  ENGINES  MUST  BE  WARMED  UP  SLOWLY.  In  general, 
the  warming  up  for  engines  of  capacities  exceeding  100  h.p.  should 
commence  15  or  20  min.  before  the  engine  is  to  be  started.  If  the  fires 


378    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 

in  the  boilers  are  just  being  started  when  it  is  desired  to  warm  the  engine, 
the  stop  and  throttle  valves  may  both  be  opened  so  that  warm  air  from 
the  boiler  will  pass  through  the  cylinders.  But  the  stop  and  throttle 
valves  should  both  be  nearly  closed  as  soon  as  the  boiler  begins  to  generate 
steam. 

NOTE. — INDEPENDENT  OR  CENTRAL  LUBRICATORS,  Y  (Fig.  432),  FOR 
THE  GUIDES,  CRANK  PIN  OR  OTHER  BEARINGS  should  be  started  just 
before  the  engine  is  started.  The  cylinder  lubricator,  X  (Fig.  432), 
should  be  started  as  soon  as  the  engine  begins  to  turn  over. 


FIG.  432. — Simple  slide-valve  automatic  engine.      (Erie  Engine  Works.) 

NOTE. — THE  TYPE  OF  GOVERNOR  MAKES  No  DIFFERENCE  IN  START- 
ING AND  STOPPING  SLIDE-VALVE  ENGINES  because  the  governor — 
whether  throttling  or  automatic — is  not  in  action  while  the  engine  is 
starting  or  stopping.  It  comes  into  play  only  when  the  engine  is  running 
near  the  speed  for  which  the  governor  is  set.  The  methods  of  handling 
Corliss-engine  governors  when  starting  or  stopping  the  engine  are 
described  in  Sec.  392. 

385.  A  Non-Condensing  Slide-Valve  Engine  May  Be 
Started  as  follows:  The  drain  cocks,  E  and  F  (Fig.  431), 
are  assumed  to  be  open,  the  stop  valve  open,  the  throttle 
just  off  its  seat,  the  lubricators  for  the  bearings  started  and 
the  engine  warmed.  Unless  there  are  by-pass  warming 
pipes,  MN  (Fig.  433),  to  both  ends  of  the  cylinder,  the  engine 
should,  in  warming,  be  rotated  or  rocked  back  and  forth  to 


SEC.  386]    RECIPROCATING-ENGINE  MANAGEMENT 


379 


By-Fhss 
Warming  Pipes 


allow  steam  to  enter  both  ends  of  the  cylinder.  The  engine 
is  then  preferably  placed  about  20  to  30  deg.  past  dead  center. 
It  is  started  by  quickly  opening  the  throttle  enough  to  carry 
the  engine  past  its  first  dead 
center.  After  the  first  dead 
center  has  been  passed,  it  may  be 
necessary  to  again  partially  close 
the  throttle  to  prevent  the  en- 
gine's speed  from  becoming  ex- 
cessive. The  speed  should  be 
kept  low  at  first  and  be  grad- 
ually brought  up  to  running 
speed  by  further  opening  the 
throttle  valve.  The  lubricator, 
X  (Fig.  432),  should  now  be 
started.  As  soon  as  the  drain  cocks,  EF  (Fig.  431),  blow  dry 
steam,  they  may  be  closed. 

386.  The  Engineer  Should  Feel  An  Engine's  Bearings  After 
It  Has  Been  Running  A  Short  Time,  say  in  from  15  min.  to 
1  hr.,  depending  on  the  load  on  the  engine.  They  should  not 

Fingers  And 
Sleeves  Out  Of 
The  Way, 
' 


FIG.  433. — Showing  by-pass  to  both 
ends  of  an  engine  cylinder  to  facili- 
tate warming. 


Path  Of 
Connecting- 
Rod  End,^ 


'Posit Ion  When 
-•'         Running  "Over" 

FIG.    434. — Showing  method  of  feel- 
ing crank-pin  bearing. 


FIG.  435. — Feeler  for  detecting  heating  of 
inaccessible  bearings.  (The  behavior  of  the 
candle  when  pushed  against  a  hot  bearing 
may  be  tested  by  pushing  it  against  a  feed- 
water  or  low-pressure  steam  pipe.) 


be  more  than  slightly  warm.  The  crank-pin  bearing  may  be 
felt  with  the  palm  of  the  hand  if  the  path  of  the  moving  connect- 
ing rod  end  is  carefully  noted  (Fig.  434),  but  care  is  necessary 


380    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 

to  avoid  being  caught  or  hit  by  a  high-speed  rod.  If  there 
seems  to  be  too  much  oil  flowing  to  any  of  the  bearings,  the 
supply  may  be  cut  down.  If  any  bearing  shows  a  tendency 
to  heat  up  to  such  a  temperature  that  the  human  hand  can- 
not be  held  on  it,  it  should  be  given  plenty  of  oil.  About  130 
deg.  fahr.  is  a  conservative  maximum  allowable  bearing  tem- 
perature. For  treatment  of  hot  bearings,  see  Sees.  412  and 
413. 

NOTE. — Where  bearings  are  inaccessible,  a  feeler  (Fig.  435)  may  be 
used.  A  little  practice  will  enable  the  operator  to  judge  the  temperature 
of  an  object  against  which  the  candle  of  the  feeler  is  pushed. 

387.  To  Stop  A  Slide-Valve  Non-Condensing  Engine,  it  is 
only  necessary  to  close  the  throttle  valve.     If  the  engine  is 
to  remain  idle  for  some  time,  the  main  stop  valve  should  be 
closed  and  all  the  oil  feeds  shut  off.     The  throttle  should  be 
left  loosely  on  its  seat  so  that  there  will  be  no  trouble  in  opening 
it  again.     If  the  stop  is  for  a  few  minutes,  the  drains,  E  and  F 
(Fig.  431),  should  be  opened  and  either  the  throttle  or  by-pass 
valves  opened  a  little  to  keep  the  engine  warm  and  drained. 
If  the  engine  is  a  hoisting  engine  operated  by  signals  from  some 
other  point,  the  engineer  should  stand  by  for  further  signals. 
If  the  signal  to  start  again  is  expected  in  a  few  seconds,  nothing 
but  the  throttle  and  perhaps  the  reversing  gear  need  ordinarily 
be  touched.     If  the  engine  is  to  be  laid  up  (see  Sec.  398)  for 
some  time,  the  drains  should  be  opened  and  be  left  open  until 
the  engine  is  started  again. 

NOTE. — NON-RELEASING  CORLISS-VALVE  ENGINES  MAY  BE  STARTED 
AND  STOPPED  IN  THE  SAME  WAY  As  ARE  SLIDE-VALVE  ENGINES.  There 
is  less  trouble  in  draining  the  cylinders  of  Corliss-valve  engines  because 
the  exhaust  valves  of  such  engines  are  so  located  that  the  condensed 
steam  drains  through  them.  These  engines  are  therefore  not  always 
provided  with  cylinder  drains.  In  starting  the  engine,  first  open  the 
throttle  valve  sufficiently  to  permit  the  engine  to  "warm  up."  Then 
close  the  throttle  and  turn  the  engine  over  by  hand  to  allow  any  con- 
densation to  flow  from  the  cylinder.  Now  open  the  throttle  just  enough 
to  allow  the  engine  to  run  very  slowly  until  it  is  thoroughly  warm. 
Then  by  further  opening  the  throttle  valve  the  engine  may  be  slowly 
brought  up  to  normal  speed. 

388.  A  Slide-Valve  Condensing  Engine  Which  Has  Sepa- 
rately Operated  Condenser  Pumps  Should  Be  Started  After 


SEC.  389]    RECIPROCATING-ENGINE  MANAGEMENT  381 

The  Pumps  Are  Started. — Where  the  condenser  pumps  are 
driven  mechanically  from  the  main  engine  they  start  simultane- 
ously with  it.  In  starting  a  slide-valve  condensing  engine, 
start  the  circulating  and  air  pumps  of  the  condenser  according 
to  directions  for  starting  non-condensing  engines  (Sec.  385). 
When  there  is  an  average  flow  of  cooling  water  through  the 
condenser  and  a  few  inches  of  vacuum  are  produced  in  it, 
the  engine  may  be  started  exactly  as  described  for  non- 
condensing  operation.  When  the  cylinder  drain  valves  are 
open,  there  will  be  little  vacuum  due  to  the  drain  valves 
admitting  air.  The  engine  may,  of  course,  be  warming  up 
while  the  condenser  is  being  started.  After  the  engine  has 
been  running  condensing  long  enough  to  give  a  constant 
temperature  in  the  condenser,  the  circulating  and  air  pumps 
may  be  adjusted  to  give  the  desired  condenser  pressure  and 
condensate  temperature.  The  condensate  temperature  should 
ordinarily  be  about  100  to  120  deg.  fahr!  The  condenser 
pressure  should  be  about  26-26.5  in.  of  mercury  vacuum  or 
about  1.5-2  Ib.  per  sq.  in.  abs. 

NOTE. — The  atmospheric  relief  valve,  G  (Fig.  430),  must,  of  course,  be 
closed  when  starting  condensing.  If  there  is  a  centrifugal  condensate 
pump,  it  may  have  to  be  primed  or  a  valve  in  the  condensate  line  closed 
before  a  vacuum  can  be  established  in  the  condenser.  If  such  a  valve 
is  closed,  it  must  be  opened  again  and  the  pump  started  as  soon  as  a 
little  condensate  accumulates  in  the  condenser. 

NOTE. — To  start  several  engines  which  have  a  common  exhaust  header 
and  condenser  (Fig.  430)  proceed  as  follows:  Start  the  engine  warming 
and  draining.  With  the  valves  in  the  exhaust  lines  from  the  engines 
closed,  start  the  condenser.  Close  the  drain  valves  and  open  the  exhaust 
line  valve  on  each  engine  just  before  it  is  started. 

389.  Condensers  Should  Be  Started  Before  Starting  The 
Main  Engine  And  Stopped  After  The  Main  Engine  Has  Been 
Stopped. — If  the  engine  is  started  first,  it  will  exhaust  out  the 
atmospheric  outlet  and  run  non-condensing.  Similarly,  if 
the  condenser  is  stopped  first,  the  atmospheric  relief  valve 
will  open  and  the  engine  will  again  run  non-condensing. 
A  certain  amount  of  oily  water  will  be  then  left  in  the  con- 
denser until  it  is  again  used. 

NOTE. — THERE  Is  ORDINARILY  LITTLE  DANGER  OF  THE  LOW-PRES- 
SURE CYLINDER  OF  THE  ENGINE  SUCKING  WATER  FROM  THE  CON- 


382    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE   [Div.  13 

DENSER  and  causing  damage.  In  a  barometric  condenser,  the  tail  pipe 
is  of  such  a  length  (over  35  ft.)  that  water  cannot  be  sucked  into  the 
exhaust  pipe.  Ejector-jet  condensers  and  low-level  jet  condensers 
(see  Figs.  350  and  352)  ordinarily  employ  vacuum  breakers  which  open 
a  valve  in  the  condenser  shell  if  the  water  level  becomes  too  high.  These 
condensers,  moreover,  are  usually  located  below  the  engines  and  so 
arranged  that  if  a  vacuum  does  form  in  the  exhaust  pipe  due  to  steam 
remaining  therein  after  the  engine  has  been  shut  down,  no  water  will  be 
sucked  into  the  cylinder.  Nevertheless,  condensate  pumps  and  wet-air 
pumps  should  always  be  run  long  enough  after  the  main  engine  has  been 
stopped  to  clear  the  apparatus  of  water. 

390.  Air  Leaks  Constitute  The  Most  Important  Source  Of 
Trouble  In  Condensing  Operation. — Leaks  may  be  detected 
by  means  of  a  lighted  candle.     The  flame  will  be  sucked  to- 
ward a   condenser   leak  since  in  the  condenser  the  pressure 
is  below   atmospheric.     Leaks   may  occur  at  valve-stem  and 
piston-rod  stuffing  boxes,  in  pipe  joints — in  fact  anywhere  in 
any  joint  holding  the  vacuum  in  the  condenser,  engine,  air 
pump  or  piping.     The  effect  of  such  leaks  is  either  to  decrease 
the  vacuum,   or  to  increase  the  power  required  by  the  air 
pump  in  maintaining  the  -vacuum,  or  both. 

NOTE. — THE  UNAVOIDABLE  DIFFERENCE  BETWEEN  THE  THEORETIC- 
ALLY POSSIBLE  VACUUM  AND  THE  ACTUAL  ATTAINABLE  VACUUM  Is 
USUALLY  LESS  THAN  %  IN.  of  mercury  in  all  large  condensers  #nd  is  a 
little  more  for  small  condensers.  The  theoretical  vacuum  is  that 
corresponding  in  a  table  of  saturated  steam  properties  to  the  temperature 
of  the  condensate  which  is  withdrawn  from  the  condenser. 

391.  Steam  Engines  Are  Stopped  In  Exactly  The  Same  Way 
Whether   Condensing    Or   Non-Condensing   as   far   as   the 
engines  themselves  are  concerned.     The  condensing  apparatus 
must  also  be  stopped  afterward.     If  there  is  a   centrifugal 
circulating  pump,  located  above  the  water  supply,  the  valves 
in  the  circulating-water  line  should  be   closed   so  that  the 
piping  will  remain  full  of  water  and  the  pump,  when  again 
started,  will  not  have  to  be  primed.     Before  leaving  a  condens- 
ing engine,  the  vacuum  should  be  broken,  that  is,  either  the 
atmospheric  relief  valve  or  some  other  valve  should  be  opened 
so  that  atmospheric  pressure  will  be  restored  in  the  condenser 
and  piping. 

NOTE. — CHANGING  FROM  CONDENSING  To  NON-CONDENSING  OPERA- 
TION is  usually  an  accident  due  to  the  condenser  becoming  heated  or  air 


SEC.  392]    RECIPROCATING-ENGINE  MANAGEMENT 


383 


bound  because  of  the  failure  of  one  of  the  pumps.  If  the  atmospheric 
relief  valve  does  not  stick,  there  will  be  no  damage  done  when  this 
happens.  The  pressure  built  up  by  the  engine,  when  the  condenser 
fails,  opens  the  valve  and  the  engine  then  exhausts  into  the  atmosphere. 
(Some  uniflow  engines  will,  when  the  vacuum  is  destroyed,  discharge 
steam  from  the  cylinder  relief  valves.  This  condition  should  be  accepted 
as  a  warning  that  the  valves  which  increase  the  clearance  volume,  Sec. 
334,  should  be  opened.)  To  intentionally  make  the  change  from  con- 
densing to  non-condensing  operation,  stop  the  condenser  pumps,  block 
open  the  atmospheric  relief  valve  if  desired  and  close  the  steam  valve  in 
the  exhaust  line  to  the  condenser.  To  change  back  to  condensing 
operation,  first  make  sure  that  the  condenser  pumps  are  working  properly 
arid  that  there  is  a  good  supply  of  circulating  water  through  the  con- 
denser. Then  gradually  open  the  steam  inlet  valve  to  the  condenser 
while  the  atmospheric  relief  valve  is  being  gradually  closed. 

392.  In  Starting  A  Simple  Detaching  Corliss-Valve  Engine, 

warm  up   as   described  for  slide-valve   engines.     Since  the 


Thumb  Screw-. 


ffl-Enlarged  Section  X-X 


Fia.  436. — Hook-rod  or  reach-rod  of  Corliss  engine  showing  latch  for  engaging  wrist- 
plate  pin.  (To  permit  wrist  pin  to  enter  or  leave  slot,  unscrew  N  until  it  leaves  its  seat, 
then  pushing  2V  to  the  left  will  also  slide  the  latch,  L,  to  the  left  and  open  the  slot.) 

exhaust  valves  of  Corliss  engines  are  usually  located  at  the 
bottom  of  the  cylinder  there  are  often  no  drain  valves  or  cocks. 
The  steam  which  condenses  in  the  cylinder  drains  through 
the  exhaust  valves  and  is  removed  by  a  trap  in  the  exhaust 
line.  In  warming  up  a  Corliss  engine,  first  unhook  the  reach 
rod  (or  hook  rod,  Figs.  436  and  437)  and  close  the  latch  so 
that  the  valves  may  be  operated  independently  of  the  eccen- 
tric. By  means  of  the  starting  lever,  L  (Fig.  438),  which  may 
be  inserted  in  a  socket  in  the  wrist  plate,  alternately  lift  the 


384    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE   [Div.  13 


admission  valves  so  as  to  admit  steam  to  both  ends  of  the 
cylinder.  At  first  not  enough  steam  should  be  admitted  to 
move  the  engine  piston ;  later,  by  rocking  the  starting  lever,  the 


Wr/sf 


Locking- 
Screw 
Handle*. 
(Attached  \ 

Ridaid/y 

ToM) 


FIG.  437. — Reach-rod  and  latch.  (This  is  another 
construction  used  for  the  same  purpose  as  that  in 
Fig.  436.  To  loosen,  first  unscrew  F  then  pull  out 
the  handle  connected  to  C.) 


FIQ.  438.  —  Corliss  engine 
starting  lever  and  wrist 
plate. 


engine  piston  may  be  caused  to  reciprocate  back  and  forth 
a  part  of  a  stroke.     When  the  engine  is  thoroughly  warm 
and  ready  for  starting,  open  the  throttle  a  little  more  and  lift 
..Throw  Lever  L  So  AS      the  proper  admission  valve 
to  start  the  engine  in  the 
desired  running  direction. 
That  is  (Fig.  439),  to  run 


To  Lift  Head  End  Va/ve- 


Pin  Above  Z_A     Uk^/ T^U       "°Ver"      ^      ^     ^^ 

shaft  W)         "ygl     steam  to  the  head  end  if 

'Crank  Shaft  rn  il      .  i  i         •       •         i 

the  crank  pin  is  above  the 

FIG.  439.— Showing  how  to  start  a  Corliss       ^ aft   and   to  thp  Prank  PnH 

engine    running     "over."     (For    engines   with  \ 

wrist  plates  of  a  construction  different  from  that  if  the  Crank  pin  is  below  the 

here  shown  it  may  be  necessary  to  move  the  cnaft        Tf  thp  Prank  i«5  IPVP! 

lever.  L,  in  the  opposite  direction  from  that  in  bndIT"       -1 

which  the  piston  is  to  move.     But  for  the  crank  with    the    shaft,   the  engine 

position  shown  in  the  above  illustration,  the  j  d       d  te  d  t 

head-end  admission  valve  should,  in  every  case, 

be  lifted  to  start  the  engine  running  over,  that  be  barred  Or  jacked  to  a  COn- 

is,  in  the  direction  indicated  by  the  arrow.)  venient     Starting     position. 

These  directions  assume  a  horizontal  engine  but  the  same 
methods  may  be  readily  applied  to  vertical  engines.  Operate 
the  valves  by  hand  until  the  engine  attains  sufficient  speed  to 
carry  it,  by  momentum,  at  least  one-half  a  revolution.  Then 


SEC.  393]    RECIPROCATING-ENGINE  MANAGEMENT  385 

slide  (swing  or  screw  according  to  the  construction  used) 
the  latch  of  the  reach  rod  so  as  to  allow  the  reach-rod  pin  to 
be  caught  and  held  properly.  Then  remove  the  starting  lever 
and  return  it  to  its  rack  and  gradually  open  the  throttle 
wider  to  bring  the  engine  up  to  speed.  After  the  engine  is 
running  at  normal  speed  and  under  control  of  the  governor 
open  the  throttle  valve  to  its  maximum  opening. 

NOTE. — IF  BY  NEGLIGENCE  THE  GOVERNOR  HAS  BEEN  ALLOWED  To 
FALL  To  THE  SAFETY  POSITION,  the  engine  will  not  start;  see  Sec.  216. 
In  stopping  after  the  preceding  run  the  gov- 
ernor should  have  been  brought  to  rest  on  the         .Governor Sleeve 
tart  cam  or  block,  B  (Fig.  440;  see  also  S,          £">_     ^^' 
Fig.  247).     If  it  is  not  on  the  cam  it  must 
be  lifted  to  the  starting  position  by  hand  or 
with    a    tackle    before    the    engine    can   be 
started.     After  the  governor  lifts,  the  start- 
ing  cam  should  fall  out  of  the  way  of  its 
own  weight.     If  it  does  not,  it  should  be  so 
turned  that,  in  case  of  an  accident,  the  gover- 
nor may  fall  to  the  safety  position. 

NOTE. — IN  STARTING  UNIFLOW  OR  POP- 
PET-VALVE ENGINES  observe  the  following 
instructions.  Poppet-valve  counterflow  en-  ,  FlG'  4f°;~  S*arJ!ng  block 

.     .  (or    cam)    for    Corliss    engine 

gines  may,  in  general,  be  started  .as  was 
directed  in  Sec.  387  for  non-releasing  Corliss 
engines.  Poppet-valve  engines  which  operate  on  high-pressure  super- 
heated steam  must  be  very  carefully  drained  as  they  are  warmed  because, 
since  the  walls  must  be  heated  to  such  a  high  temperature,  condensation 
during  warming  will  be  very  rapid.  For  this  reason,  such  engines  should 
be  very  slowly  started.  In  starting  a  uniflow  engine,  first  drain  all  water 
from  the  steam  manifold,  cylinder  heads  and  exhaust  cages.  Then  close 
the  drains  and  "crack"  the  throttle  so  that  these  parts  may  be  warmed 
by  the  live  steam.  After  ten  or  fifteen  minutes  again  open  all  drains. 
Then  turn  the  engine  so  that  its  crank  is  a  little  ahead  of  dead  center  and 
open  the  throttle  a  little,  leaving  the  drains  open  for  a  few  minutes  so 
that  all  water  may  flow  from  the  engine.  Immediately  after  opening 
the  throttle  turn  on  the  oil  to  all  bearings.  Allow  the  engine  to  run  slowly 
for  some  minutes  while  all  lubrication  may  be  inspected  for  proper  action. 
A  new  engine  should  be  speeded  up  only  in  the  course  of  two  or  three 
hours  and  all  of  its  bearings  should  be  left  loose  so  as  to  peen  themselves 
to  a  better  wearing  surface. 

393.  In  Stopping  A  Detaching  Corliss  Engine,  throw  the 
starting  cam  or  block  (5,  Fig.  440)  of  the  governor  into  the 

25 


386     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 


starting  position  before  or  immediately  after  turning  off 
the  steam.  The  governor  will  then  come  to  rest  on  the  cam 
and  be  in  proper  position  for  starting  again.  On  some  engines — 
the  Vilter  for  example — there  is  a  rod,  running  from  the  governor 
starting  cam  to  the  throttle  valve,  which  automatically  places 
the  starting  block  in  the  starting  position. 

394.  In  Starting  A  Compound  Corliss  Engine,  it  is  neces- 
sary to  warm  both  cylinders.  There  is  usually  a  by-pass,  P 
(Fig.  441),  or  pass-over  valve  for  admitting  live  steam  to  the 
receiver,  from  which  the  steam  will  pass  to  the  low-pressure 


By-Pass  To Receiver $    :    g 

Hiah-Pressure    \  \ 
Cylinder---^ 


Generator  . . 

Live- 

-  Fly  wheel  Steam''' 

Low-Pressure  Header 

Cylinder--^ 


'Trap 

Reservoir  for 
Separator 


'Drain  From  Receiver         ''Exhaus  t 
>  Header 

'  'Drain  Line 


FIG.  441. — Some  typical  piping  for  a  large  compound  engine. 

cylinder.  Thus  this  by-passed  steam  warms  both  the  receiver 
and  the  low-pressure  cylinder.  The  low-pressure  and  high- 
pressure  cylinders  may  therefore  be  warmed  simultaneously 
about  as  explained  for  simple  engines  in  Sec.  392.  The  drain, 
D,  on  the  receiver  should  be  opened  if  not  already  so.  The 
by-pass  valve  in  P  is  given  only  a  slight  opening  so  that  a  high 
pressure  will  not  be  produced  in  the  receiver.  A  cross-com- 
pound engine  may  usually  be  started  by  opening  the  throttle. 
If  the  high-pressure  piston  is  on  dead  center,  open  the  by- 
pass valve  in  P  sufficiently  to  give  several  pounds  receiver 
pressure;  then  the  low-pressure  piston  will  usually  start  the 
engine.  If,  after  opening  the  valve  in  P,  the  engine  does  not 
start,  then  either  the  cut-off  is  so  early  that  no  admission  valve 


SEC.  395]    RECIPROCATING-ENGINE  MANAGEMENT  387 

is  open  or  there  is  excessive  friction.  If  no  admission  valve 
is  open,  then  one  of  the  admission  valves  must  be  opened  by 
lifting  its  dash-pot  piston  with  a  starting  lever.  If  now  the 
engine  does  not  start,  there  being  ample  steam  pressure  and 
throttle  opening,  the  friction  is  excessive  or  it  is  jammed. 
A  bearing  may  have  seized  or  the  piston  become  rusted  in 
or  jammed  in  the  cylinder.  Tandem-compound  engines  are 
started  just  as  are  simple  engines  but  for  them  only  the  high- 
pressure  cylinder  valves  need  be  operated  by  hand. 

NOTE. — IF  THERE  Is  No  BY-PASS  VALVE  ON  A  COMPOUND  ENGINE, 
steam  must  be  worked  into  the  low-pressure  cylinder  by  working  the 
high-pressure  cylinder  valves.  The  low-pressure  cylinder  does  not  need 
to  be  as  warm  as  the  high-pressure  cylinder  because  it  will  operate  at  a 
lower  temperature. 

NOTE. — TANDEM-COMPOUND  SLIDE-VALVE  ENGINES  ARE  STARTED 
just  as  are  simple  slide-valve  engines  except  that  the  low-pressure 
cylinder  must  also  be  warmed,  drained  and  oiled.  Cross-compound 
slide-valve  engines  are  started  similarly  also;  but  such  engines  will 
nearly  always  start  when  the  throttle  and  by-pass  are  opened.  The 
use  of  the  receiver  is  the  same  as  explained  above  under  compound  Corliss 
engines. 

395.  Compound  And  Multi-Expansion  Engines  Are  Stopped 
As  Are  Simple  Engines,  by  closing  the  throttle.     The  only 
difference  in  the  starting  and  stopping  of  multi-expansion 
engines  is  in  the  greater  number  of  parts  to  be  taken  care  of.     As 
far  as  oiling  and  draining  are  concerned,  each  cylinder  of 
a  multi-expansion  engine  may  be  treated  as  a  simple  engine, 
although  there  is  usually  a  central  force-feed  lubricator  for 
multi-expansion  engines;  Sec.  507. 

NOTE. — CONDENSING  OPERATION  OF  COMPOUND  ENGINES  requires 
no  special  explanation  beyond  that  already  given.  The  low-pressure 
cylinder  is  the  only  one  directly  affected  by  the  condenser.  For  more 
complete  directions  for  condenser  maintenance,  see  the  author's  STEAM 
POWER  PLANT  AUXILIARIES  AND  ACCESSORIES. 

396.  Regular  Inspection  Trips  Should  Be  Made  Through 
A  Power  Plant  At  Least  Once  Each  Hour. — All  equipment 
for  which  the  engineer  is  responsible  should  be  examined  on 
such   trips.     On   these   inspection   trips,   listen   for   unusual 
sounds  and  knocks,  feel  for  hot  bearings,  and  look  for  leaks  of 
all  sorts.     The  oil  supply  in  all  oil  cups  and  lubricators  should 


388    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 

be  replenished  if  likely  to  be  necessary  before  the  next  trip. 
See  that  oil  is  being  fed  properly  to  the  cylinders  and  bearings. 
Watch  the  boiler  pressure  to  insure  that  the  fireman  is  keeping 
a  good  steam  supply.  Note  the  condenser  pressure  as  an 
indication  of  the  condenser  action.  In  short,  check  up  every 
readily  observed  factor  and  detail  which  may  influence  the 
operation  of  the  plant.  An  engineer  should  not  leave  the 
plant  during  his  shift  unless  it  is  in  charge  of  a  competent 
assistant  because  trouble  may  occur  at  any  instant  when 
power-plant  machinery  is  running. 

397.  In  Cleaning  Engines,  do  not  use  any  emery  or  abrasive 
material  which  may  get  into  the  bearings  and  cause  trouble. 
Various  polishing  powders  which  are  free  from  grit  are  on  the 
market  and  are  preferred  for  this  purpose.     An  engine  should 
be  cleaned  immediately  after  it  has  been  stopped — this  is  the 
best  time.     Water  will  spot  the  polished  parts  of  engines  if 
it  is  allowed  to  stand  on  them.     The  polished  parts  should 
be  left  covered  with  a  thin  film  of  oil.     The  oil  will  in  a  damp 
atmosphere  prevent  corrosion  of  the  metal. 

398.  Laying  Up  An  Engine  consists  in  preparing  it  so  that 
it  will  not  suffer  any  ill  effects  from  lying  idle  for  a  year  or 
more  if  undisturbed.     If  the  piston  and  valve  rods  are  steel 
and  soft  packing  is  used,  either  the  rod  or  the  packing  must  be 
removed.     If  not  removed  the  water  with  which  the  packing 
is  saturated  will  corrode  the  rod.     If  the  engine  was  supplied 
with  plenty  of  oil  at  the  end  of  its  last  run  and  was  well 
drained  while  hot,  the  cylinder  interior  will  thereby  be  ordi- 
narily sufficiently   protected.     It   will   not  be   necessary  to 
remove  the  head.     It  is  a  safe  plan  to  remove  slide  valves  and 
coat  them  and  their  seats  with  grease.     The  polished  metal 
parts  should  be  also  coated  with  grease. 

NOTE. — IF  AN  ENGINE  Is  To  BE  IDLE  FOR  ONLY  A  FEW  DAYS  but  is 
not  to  be  laid  up,  it  is  advisable  to  run  it  for  half  an  hour  each  day  during 
the  period  to  preserve  the  oil  films  on  the  cylinder  walls  and  on  the  piston 
and  valve  rods. 

399.  Engines   Should   Not    Ordinarily   Need  Overhauling 
More   Often   Than   Once  A  Year  even  if  they  are  in  con- 
tinuous service.     Engines  are  more  commonly  run  for  several 
years  before  being  completely  overhauled. 


SEC.  400]    RECIPROCATING-ENGINE  MANAGEMENT  389 

400.  Piston  Rings  Must  Sometimes  Be  Replaced. — If  exces- 
sive leakage  past  the  piston  is  detected  (see  following  note) 
it  is  probably  due  to  worn,  broken  or  poorly  fitted  rings. 
Loose  or  broken  rings  may  sometimes  be  detected  by  the 
rattling  sound  when  the  engine  is  running.  Broken  rings 
should  be  replaced  as  soon  as  detected  to  avoid  scoring  of 
the  cylinder  walls  by  the  broken  ends.  Methods  of  replacing 
them  will  be  described  in  the  following  sections. 

NOTE. — To  TEST  FOB  VALVE  LEAKAGE  OF  SINGLE-VALVE  ENGINES 
(Power,  March  1,  1921)  proceed  as  follows:  A  general  test  of  tightness  can 
be  made  by  turning  the  engine  over  to  such  a  position  that  the  valve 
covers  the  ports  of  both  ends  of  the  cylinder  at  the  same  time.  Then, 
upon  admitting  steam  at  the  throttle  valve,  leakage  will  be  shown  by 
discharge  of  steam  from  open  cylinder  pet  cocks  or  indicator  connections, 
or  by  escape  of  steam  from  the  exhaust  pipe. 

The  leakage  under  running  conditions  can  be  approximately  determined 
by  blocking  the  flywheel  and  making  tests  at  different  points  of  stroke  of 
the  piston. 

To  test  valve  leakage  of  a  throttling,  D-slide-valve  engine  at  a  given  point 
of  piston  stroke  from  the  crank  end  of  the  cylinder,  remove  the  cylinder  head 
and  with  the  piston  in  the  crank  end  of  the  cylinder,  turn  the  flywheel  in 
the  running  direction,  and  block  the  wheel  when  the  piston  has  arrived 
at  the  desired  point;  then  gradually  admit  steam  through  the  throttle  and 
observe  whether  there  is  escape  of  steam  from  the  steam  passage  of  the 
head  end  into  the  cylinder  or  out  of  the  exhaust  pipe. 

Piston  leakage  must  be  corrected  before  it  is  attempted  to  inspect  leakage 
of  the  valve  when  it  is  in  position  for  admission  of  steam  for  a  piston  stroke 
from  the  head  end  of  the  cylinder,  because  the  crank  end  of  the  cylinder 
cannot  be  uncovered  to  distinguish  piston  leakage  from  valve  leakage. 
When  the  piston  packing  has  been  made  tight  and  cylinder  head  replaced, 
turn  the  flywheel  in  the  running  direction  until  the  piston  has  arrived  at 
the  desired  point  of  stroke  from  the  head  end  of  the  cylinder.  Then  with 
the  wheel  blocked,  open  the  throttle  a  little,  and  steam  escaping  from  the 
exhaust  pipe,  or  the  cylinder  pet  cock  or  indicator  connection  of  the 
crank  end,  will  indicate  the  valve  leakage. 

With  a  single-valve  automatic  engine,  proceed  the  same  as  for  testing 
valve  leakage  of  a  throttling  engine,  but  with  the  governor  blocked  in  its 
average  running  position,  and  in  positions  giving  other  points  of  cut-off  at 
which  it  is  desired  to  test  valve  leakage. 

401.  To  Replace  A  Cast-Iron  Snap  Piston  Ring,  proceed  as 
follows:  The  piston,  of  course,  must  be  removed  from  the 
cylinder  and,  if  small,  may  be  held  in  a  vise  (Fig.  442).  The 
old  ring  is  first  pried  out  as  shown  in  Fig.  443  by  means  of  a 


390    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 


file  and  a  strip  of  sheet  iron  or  piece  of  hack-saw  blade,  B. 
The  prying  may  be  continued  and  other  strips,  B,  inserted 
until  the  ring  may  be  slipped  off.  The  groove  is  now 
examined  and  if  it  appears  to  be  worn  out  of  shape  as  is  groove 


Removable  Copper  ,--. — *• 

Pktonfbd.-.^  *»*•>  -Pl5ton 


.-Sheet  Iron  Strip 

"~ Packing 


Benc/7- 


FIG.  442. — Piston    rod    held  in   vise    for   con-     FIG.  443. — Prying  end  of  packing  ring 
venience  in  replacing  snap  ring.  out  of  groove. 

A  (Fig.  444)  it  should  be  trued  up  on  a  lathe  so  that  its  sides 
are  flat  as  are  those  of  groove  B. 

402.  A  Piston  Ring  Must  Be  Fitted  To  The  Piston  Grooves 
as  shown  in  Fig.  445.     If  a  complete  snap  ring  is  on  hand,  it 


S/ofes  Of  Groove 

•-•Intact,  Due  To  Snug 

Fit  Of  Snap  R/'ny 


Stoles  Of  Groove . 
Distorted  By  Pounding 


FIG.  444. — Illustrating  wearing  effect      FIG.    445. — Illustrating    fit    of    snap    ring    in 
of  poorly  fitted  snap  ring.  piston  groove. 

is  only  necessary  to  grind  it  to  the  correct  width  and  slip  it  on. 
If  the  rings  on  hand  are  solid  rings  (Fig.  446) ,  it  is  well  to  grind 
or  machine  them  to  the  correct  width  before  slotting  them. 


SEC.  402]    RECIPROCATING-ENGINE  MANAGEMENT 


391 


Since,  in  time,  the  piston  grooves  wear  wider,  rings  which  are 
kept  for  replacement  should  be  a  few  thousandths  of  an 
inch  wider  than  the  grooves  and  should  be  ground  or  machined 
to  fit.  If  machine  tools  are  available,  they  should  be  used. 


Finishing  Nail  To  Be  Driven  Below  Eotgre  Of  Ring-. 


k- 


Fia.    446.  —  A    solid     cast-iron         FIG.  447. — Packing  ring  fastened  down  for  filing, 
snap  ring. 

A  few  thousandths  of  an  inch  of  metal  may,  however,  be 
removed  with  a  file. 

EXPLANATION. — The  ring  may  be  nailed  to  a  board  for  filing  as  shown 
in  Fig.  447.  If  there  is  more  than  about  0.010  in.  of  metal  to  be  removed, 
it  usually  pays  to  start  filing  with  a  flat  bastard  file  (Fig.  448)  and  finish 


Cast-Iron  Pack, 


\  I  About  fig  Over  ^ 
Width  Of  Piston ' 
Groove 


FIG.  448. — Cast-iron  packing  ring  in  position  for 
filing. 


FIG.  449.— Outside  caliper 
for  measuring  width  of  cast- 
iron  packing  ring. 


with  a  fine  single  cut  file.  The  calipers  (Fig.  449)  are,  for  convenience, 
set  at  about  1/100  in.  over  the  correct  size  for  the  rough  filing.  When 
the  ring  is  nearly  down  to  size,  it  should  be  finished  by  testing  with  a 
surface  plate  (Fig.  450).  Only  one  side  of  the  ring  should  be  filed.  The 
other  side,  being  true,  should  be  left  undisturbed  as  a  reference  plane 


Octagon  Sfeef  Scrofpet..^ 


392    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Drv.  13 

from  which  to  measure.  The  surface  plate  is  coated  with  a  thin  film  of 
red  lead  and  oil  and  the  ring  is  wiped  clean  and  rubbed  on  the  plate. 
(Prussian  blue  is  preferable  to  red  lead  but  is  more  expensive.)  Where 
the  red  lead  rubs  on  the  ring,  the  ring  is  high  and  should  be  further 
reduced  with  a  file  or  scraper  (Fig.  451).  This  procedure,  if  continued 
until  the  ring  bears  evenly  on  the 
plate,  will  insure  a  true  surface  on  the 
ring. 

NOTE. — SMALL  PISTON  RINGS  MAY 
BE  GROUND  To  SIZE  by  rubbing  on 
a  piece  of  emery  cloth  tacked  to  a 
flat  board  or  glued  to  a  flat  plate 
(Fig.  452).  For  the  most  accurate 
work,  a  lapping  plate  (Fig.  453)  is 
used.  The  grooves  in  the  plate  are 
filled  with  a  lapping  compound  of 


.-Lifting  Lugs-... ^ 
••True  Facing  Surface' 


Fia.    450.  —  Cast-iron     face     or    surface     FIG.  451.  —  Cast-iron  packing  ring  in  po- 
plate.  sition  for  scraping  to  fit. 


emery  and  oil.  The  ring  is  rubbed  over  the  plate  and  the  compound 
which  runs  from  the  grooves,  gets  between  the  ring  and  the  plate  and 
grinds  the  ring  to  size. 

f-Sbts  To  Be  Filled  With  Oil  And  Emery  ~.^ 
{Cast-Iron  Packing  Ri'ny 


FIG.     452.  —  Cast-iron  packing  ring 
ground  down  on  emery  cloth. 


Cast-Iron  Pfafe"'  Wooden  Fro/me--' 

FIG.  453. — A  lapping  plate. 


403.  Solid  Piston  Rings  Must  Be  Cut  To  Allow  Springing 
Into  Place. — Common  snap  rings  are  often  turned  eccentric 
so  that  they  are  thinner  at  one  side  than  at  the  other.  They 
are  cut  by  means  of  a  hack-saw  at  their  thinnest  section  as 
shown  in  Fig.  454.  The  length  of  the  segment  thus  removed 


SEC.  404]    RECIPROCATING-ENGINE  MANAGEMENT 


393 


Scn'beol  Lines-1 
Segment  Of  Ring-- 


is  the  difference  between  the  circumference  of  the  ring  and  that 
of  the  cylinder.  If  the  ring  is  not  to  be  fitted  as  explained 
below,  the  ends  should  be  filed  down  so  that  they  will  be  about 
J^2  m-  apart  when  the  ring  is  in  place  in  the  cylinder.  The 
solid  rings  are  usually  made  about  2  per 
cent,  larger  in  diameter  than  the  cylinder.  Len&th( 

NOTE. — A  FINISHED  RING  MAY  BE  TESTED 
FOR  FIT  in  the  cylinder  before  it  is  sprung  onto 
the  piston.  A  coating  of  red  lead  on  the  cylinder 
walls  will,  when  the  ring  is  rubbed  on  it,  show 
what  portions  of  the  ring  bear  on  the  wall. 
These  portions  should  be  slightly  reduced  by 
draw-filing.  This  operation  will  cause  the  ends  to  snap  packing  ring, 
spring  apart  so  that  they  will  have  sufficient  play. 

404.  Worn  One-Piece  Piston  Rings  May  Be  Expanded  To 
Snug  Contact  With  The  Cylinder  Wall  By  Peening.— This  is 
done  by  holding  the  ring  on  an  anvil  or  heavy  face-plate 
(Fig.  455)  and  striking  its  inner  surface  repeatedly  with  the 
peen  of  a  ball-peen  hammer.  The  ring  should  make  solid 
contact  with  the  surface  on  which  it  rests,  and  each  blow  of 
the  hammer  should  be  directly  above  the 
point  of  contact.  The  blows  should  be 
comparatively  light  and  of  equal  intensity. 
The  peening  operation  should  begin  at 
one  end  of  the  ring  (Fig.  455)  and  should 
progress  around  the  inner  face  to  the  other 
end.  The  hammer  blows  should  not  ap- 
proach either  edge  of  the  ring  nearer  than 
about  %  in. 

405.  The  Repair  Of  Steam-Engine  Valves 
is   necessary  whenever  the  valves  are  so 
badly  worn  that  steam  leakage  past  them 
is   excessive.     The   repair  always  consists 
FIG.  455.— Peening  a  cast  of:  (1)  Truing  up  the  surface  along  which 

iron  snap  packing  ring.      .-,          1)n]1)f><*      <*pnf         (<}\       Mnkinn     t~hf>    Kroner 

vtd\j        (/LH/Ut/b        oc/Cvi/»          \£i J        J.VA.  {Jilvv  fv\J        ltll/\j      L/l  \JlJ\jt 

adjustment  so  that  the  surfaces  are  kept  together  as  they  should  be. 
These  repairs  are  explained  below  for  the  various  valves. 

EXPLANATION. — REPAIRING  PLAIN  D-SLIDE  VALVES  involves  a  resur- 
facing of  the  valve  and  its  seat.     Usually  the  valve  can  be  finished  in  a 


394     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 

shaper  or  miller,  but,  if  machine  tools  are  not  available,  it  may  be  scraped 
to  a  true  surface.  A  surface  plate  (Fig.  450)  is  coated  lightly  with  a  red- 
lead-and-oil  mixture  and  the  valve  rubbed  lightly  on  it.  The  high  spots 
of  the  valve  face,  which  are  now  marked  with  red  lead,  may  be  scraped 
off  with  a  scraping  tool  (see  Figs.  451  and  467).  (If  deep  grooves  appear 
in  the  valve  face,  the  high  spots  may  first  be  filed  off.)  Each  time  the 
high  spots  are  removed  the  valve  should  again  be  tried  on  the  surface 
plate,  continuing  these  processes  alternately  until  the  entire  face  of  the 
valve  is  marked  when  applied  to  the  surface  plate.  The  valve  may, 
after  its  face  is  true,  be  cleaned  and  itself  coated  with  red  lead.  It 
should  then  be  applied  to  the  valve  seat  so  as  to  mark  the  high  spots  on 
the  seat.  These  may  then  be  scraped  off  until  a  true  fit  is  established 
between  the  valve  and  its  seat.  Oil  grooves  may  be  cut  into  the  valve 
seat  if  desired,  but  they  must  not  extend  quite  to  the  working  edges  of  the 
seat  lest  they  should  provide  passages  for  steam  to  blow  through.  Plain 
D-slide  valves  require  no  adjustment  to  keep  the  surfaces  together. 
The  steam  pressure  outside  the  valve  insures  good  contact. 

IN  REPAIRING  BALANCED  SLIDE  VALVES,  the  cover  plate  and  the  valve 
surface  which  rubs  against  it  must  also  be  fitted  as  is  the  valve  against  its 
seat.  If  machine  tools  are  available,  the  surfaces  may  be  readily 
machined.  Otherwise,  all  surfaces  must  be  scraped  (or  filed)  to  fit  as 
directed  above.  The  cover  plate  must  then  be  so  adjusted  that  it  bears 
lightly  against  the  valve.  In  some  engines,  screws  are  provided  for 
this  adjustment.  In  others,  the  cover  plate  is  held  from  the  valve  seat 
by  distance  pieces  which,  to  provide  adjustment,  must  be  filed  down. 
Great  care  must  be  exercised  in  such  engines  that  too  much  metal  is  not 
removed  as  this  would  necessitate  using  shims  under  the  distance  pieces. 
To  test  the  cover-plate  adjustment  place  a  piece  of  thin  (tissue)  paper 
between  it  and  valve.  If,  now,  the  valve  can  be  moved  by  hand  while 
pressure  is  applied  to  the  cover  plate  (by  having  an  assistant  press  against 
it  firmly  with  both  hands)  the  cover  plate  is  too  far  from  the  valve. 
Adjust  until,  with  the  paper  in  place,  the  valve  cannot  easily  be  moved. 
Then  see  that,  with  the  paper  removed,  the  valve  slides  freely. 

THE  REPAIR  OF  PISTON  VALVES  usually  necessitates  the  replacement 
of  the  valve  or  its  seat,  although  some  piston  valves  are  capable  of 
adjustment.  Sometimes,  when  wear  is  not  excessive,  leaks  may  be 
stopped  by  simply  refitting  the  rings  in  the  valve  (Sec.  400).  If  this  will 
not  suffice,  see  if  the  valve  is  adjustable.  If  it  is,  adjust  it  so  that  the 
wear  is  compensated  for.  If  the  valve  is  not  adjustable,  determine 
whether  the  wear  is:  (1)  All  on  the  seat.  (2)  All  on  the  valve.  (3)  On 
both  the  valve  and  the  seat.  If  either  the  valve  or  seat  is  made  of  brass, 
the  wear  will  probably  be  on  the  brass  part.  The  brass  part  can  then 
be  removed  and  replaced  with  a  new  piece.  (These  pieces  should  be 
kept  on  hand.)  If  the  valve  and  seat  are  both  worn,  the  seat  must  be 
rebored  and  the  valve  must  be  replaced  by  a  larger  one.  In  event  of  any 
replacement,  the  valve  and  seat  should  be  ground  to  fit  by  introducing 
fine  emery  powder  and  oil  between  them  and  working  them  upon  each 


SEC.  406]    RECIPROCATING-ENGINE  MANAGEMENT 


395 


Mandre/-. 


other  until,  when  clean,  they  slide  freely.     The  emery  powder  must  then 
be  very  carefully  cleaned  out  so  that  it  cannot  be  carried  into  the  cylinder. 

THE  REPAIR  OP  CORLISS  VALVES  is  most  effectively  accomplished  by 
boring  out  the  valve  seats  and  procuring  from  the  manufacturer  new 
valves  of  the  proper  size  to  fit  the  newly  formed  seat.  For  reboring  the 
seat,  a  jig,  somewhat  similar  to  that  shown  in  Fig.  464,  may  be  employed. 
(Engine  manufacturers  usually  have  such  jigs.)  The  new  valve  may 
then  be  "ground  in"  as  explained  above  for  piston  valves.  If  reboring 
is  not  deemed  necessary  or  advisable,  the  valves  may  simply  be  fitted 
by  marking  with  red  lead  and  scraping  or  filing  until  a  tight  fit  is  obtained. 

THE  REPAIR  OF  POPPET  VALVES  should  scarcely  ever  be  necessary 
because  these  valves  are  not  subjected  to  rubbing  action.  However, 
should  refitting  be  necessary,  the  valve  springs  and  cages  may  be  removed 
and  the  seats  coated  lightly  with  a  mixture  of  fine  emery  and  oil.  The 
valve  may  then  be  placed  upon  the  seat  and  rotated  back  and  forth 
through  a  small  angle  for  two  or  three  minutes.  The  valve  should  then 
be  removed,  the  valve  and  seat  cleaned  off,  and  inspected  to  see  if  a  clear 
bright  ring  is  obtained  completely  around  each  seat.  If  the  surfaces 
are  not  satisfactory,  the  grinding  process  should  be  repeated  until  they 
are.  It  is  preferable,  in  grinding 
poppet  valves,  to  grind  the  valves 
immediately  upon  shutting  down  the  Distance  Piece-. 
engine  and  before  the  valves  or  seat 
have  a  chance  to  cool  off. 

406.  Re-Babbitting  May  Be 
Necessary  Where  Bearings 
Have  Been  Partially  Melted 
Out  (Fig.  456),  due  to  heating 
of  the  bearings  while  the  engine 
was  in  operation.  Also  the 
normal  running  wear  in  the 
bearings  may  necessitate  their 
eventually  being  re-babbitted. 
A  bearing  should  preferably 
be  removed  from  the  engine  for  re-babbiting.  The  general 
procedure  is  to  pour  melted  babbitt  metal  into  the  shells  of 
the  bearing,  one  at  a  time,  using  a  mandrel  to  form  the  inner 
surface  of  the  babbitt.  The  mandrel  is  smaller  than  the 
shaft  so  that  the  surface  of  the  metal  may  be  accurately 
finished  to  fit  the  shaft.  Pouring  the  metal  around  the  shaft 
is  not  recommended.  When  it  is  done,  thick  shims  should  be 
be  used  between  the  halves  of  the  bearing  so  that  the  surface 


Wooden B/ocks'         '-Flange  Of Manc/re/ 
FIG.  456. — Pouring  a  main  bearing  box. 


396    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 


of  the  babbitt  may  be  scraped  and  the  play  may,  when  the 
bearing  is  assembled  for  service,  be  taken  up  by  using  a  thinner 
shim. 

407.  To  Dismantle  A  Quartered  Main  Bearing  (Fig.  457) 
for  re-babbitting,  the  cap,  M ,  and  top  shell,  S,  are  first  removed 
and  the  quarter  boxes,  Q,  are  drawn  out.  Shop  marks,  A  and  B, 
which  indicate  the  proper  position  of  the  bottom  shell, 
will  generally  be  found  on  the  end  of  the  shell  and  on  the 
bearing  pedestal.  These  marks  should  coincide.  Before 
the  bottom  shell  can  be  removed,  it  will  generally  be  necessary 


Eccentric  Slipped 
From  Normal  Position. 
Normal  Position 
Quarter  Of  Eccentric-.        ; 


\       ''Adjusting 
Pillow  Block-'          '.         Wedge 

'Line  Of  Square 
[FIG.  457. — A  quartered  main  bearing. 


'^ Pair  Of  Jacks 


FIG.  458. — Main  shaft  jacked  up  to  permit 
removal  of  bottom  bearing  shell. 


to  slip  the  eccentric  and  possibly  the  flywheel  along  the  shaft. 
The  nuts  on  the  outboard  bearing  may  then  be  slacked  off 
and  the  shaft  raised  from  the  bottom  shell  with  jacks  J  (Fig. 
458),  placed  under  the  crank  and  outer  end  of  the  shaft. 
This  will  permit  the  bottom  shell  to  be  drawn  out. 

408.  To  Re-Babbitt  The  Boxes  Of  A  Quartered  Main 
Bearing,  after  the  boxes  have  been  taken  from  the  pillow 
block,  the  old  babbitt  metal  should  first  be  chipped  and  pried 
from  the  boxes  with  cape  and  flat  chisels.  Each  box  may 
then  in  turn  be  clamped  for  babbitting  (Figs.  456  and  459) 
to  a  mandrel  having  a  diameter  about  ^{Q  in.  smaller  than 
the  shaft  diameter.  A  piece  of  iron  or  steel  pipe  screwed 
into  a  flange  (Fig.  460)  and  finished  in  the  lathe  makes  an 
excellent  mandrel  for  this  purpose.  The  wooden  blocks, 
A,B,C  and  D  (Figs.  456  and  459) ,  should  be  cut  and  the  clamps 


SEC.  409]       RECIPROCATING-ENGINE  MANAGEMENT          397 


adjusted  as  shown.  Where  the  boxes  cannot  be  removed 
from  the  engine  they  may  be  re-babbitted  as  shown  in  Figs. 
461  and  462. 


.flange  Of 
'  Mandrel 


Double  Extra 
Heavy  Iron  Pipe*, 


Cast  Iron  Shell     ./ 

Of  Top  Box,  Of        'Clamp 

Main  Bearing 

FIG.  4  5 9.  —  Main-bearing    box 
clamped  to  babbitting  mandrel. 


FIG.    460. — Mandrel    for    use    in 
main  bearings. 


Cast  /ron  Flange 

babbitting 


NOTE. — MAIN  BEARING  BOXES  SHOULD  BE  BABBITTED  WHILE  WARM. 
This  will  prevent  sputtering  and  blowing  of  the  metal  when  poured  and 
will  facilitate  the  running  of  the  metal  to  all  parts  of  the  box.  Good 

Gates  And  Vents 

For  Pour  ing  Formed 
By  Removing], 


^  

o 

W- 

-4 

0 

Moulding 
^Sand  '•'• 

8 

i 

:'•:  Or  •.'•. 

CQ 

ii 

Tire-.'-' 

^ 

Clay'-  • 

0 

• 

ol 

r 

iii 

c 

c    *  ^-<i_  j, 

^             t"~~~J             I 

I-  P I  a  n  V  i  e  w 


Closing  Strip'  ''Babbitt  Recess 

E-End  Elevation 

FIG.  461. — Tamping  of  journal  with  molding  sand  or  fire  clay.  The  plugs,  P,  are 
withdrawn  and,  after  the  ends  of  the  babbitt  recess,  R,  are  closed  with  wooden  collars,  C, 
the  bearing  may  be  poured. 

results  may  generally  be  assured  if  the  box  is  warmed  to  a  temperature 
of  about  150  deg.  fahr.  before  it  is  clamped  to  the  mandrel. 

NOTE. — THE  OBJECT  OF  POURING  A  MAIN  BEARING  Box  IN  A  VERTI- 
CAL POSITION  (Fig.  456)  is  to  prevent  shrinkage  holes  from  forming  in  the 


398    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 


babbitt.     Shrinkage  holes  will  almost  invariably  result  if  a  large  bearing 
is  poured  in  a  horizontal  position. 


Wooden  Plua 

Or  Riser--  ^ 
To  Form  Gate    P "'. 


.Main 
•'  Shaft 


Notches  Cut 
In  Wood  Strip 


Pillow  Block-' 
\       'Wooden  Strip 
''Babbitt  Recess 


FIG.  462. — Showing  method  of  closing,  gating,  and  venting  babbitt  recess  in  pillow 
block  when  re-babbitting  a  non-removable  bottom  shell.  A  bearing  so  prepared  is 
tamped  with  moulding  sand  or  fire  clay  as  shown  in  Fig.  461.  The  plugs,  P,  are  set  into 
notches  in  A  and  B,  which  notches  later  form  gates  for  the  babbitt. 


409.  Freshly  Re-Babbitted  Bearings 
Should   Be   Peened  And   Finished.— 

The  metal  should  be  forced  tightly 
into  the  grooves  (Fig.  463)  by  striking 
the  inner  surface  with  a  peening  ham- 
mer as  shown.  The  bearing  should 
then  be  bored  to  size  with  a  jig  (Fig. 


Ball-Peen 
Hammer. 


Feed 
Screw. 


Line  Of  Square '' 

FIG.    463. —  "Peening    in"    a    main- 
bearing  box. 


Plank-' 


-HeadStock     i 
Bottom  Box  ' 


FIG.  464. — Improvised  jig  for  bor- 
ing babbitted  bearing  boxes. 


464)  or  on  a  lathe.     Now,  three  or  four  oil  grooves  (Fig.  465) 
about   J4   in.   wide   should  be  chiseled  (Fig.  466)  or  filed  in 


SEC.  409]    RECIPROCATING-ENGINE  MANAGEMENT 


399 


the  babbitt  to  distribute  the  oil  from  the  oil  holes  over  the 
face  of  the  bearing.  The  edges  of  the  grooves  should  be 
chamfered.  Finally,  the  bearing  should  be  "  scraped  in. " 

EXPLANATION. — IN  SCRAPING  A  BEARING,  Fig.  467,  a  portion  of  the 
shaft  is  coated  with  a  very  thin  layer  of  red  lead  and  oil.  The  bearing  is 
then  placed  against  the  coated  portion  of  the  shaft  and  rotated  a  few 


Top  Shell 


Section  Through  A-B 


Bottom  Shell 


FIG.  465. — Correct  oil  grooves  for  main  bearing.  Note  that  the  grooves  are  cut  for 
a  given  direction  of  rotation.  They  first  distribute  the  oil  and  then  re-collect  it  to 
prevent  it  from  running  from  the  ends  of  the  bearing.  Only  the  leading  edges  of  the 
bearing  shells  are  chamfered. 

degrees  around  the  shaft.  The  "high  spots"  of  the  bearing  (Fig.  467) 
are  thus  coated  with  the  red  lead.  Then  with  a  scraper  these  high  spots 
are  scraped  off.  Care  must  be  exercised  to  insure  that  the  scraping  tool 
does  not  cut  deep  into  the  babbitt  metal.  The  shaft  should  again  be 
coated — by  spreading  the  red  lead  to  the  spots  from  which  it  was  removed 
— and  the  bearing  again  applied  to  it.  It  will  be  noted  that  now  more 
high  spots  appear  than  before.  These  are  again  removed  by  scraping. 
After  repeated  scraping  and  marking  it  will  be  found  that  the  bearing 
will  bear  marks  all  over  its  surface  and  that  the  unmarked  surface  is 


400    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 


very  small.  When  no  large  unmarked  surface  appears,  the  bearing  is 
ready  to  be  placed  in  position  on  the  engine.  Bearings  which  are 
properly  scraped  will  need  little  " running  in"  and  are  not  likely  to  heat 
or  knock  when  properly  adjusted. 


Round-Hose 
Chisel 


High  Spots 
Indicated  By 
Red  Lead 
On  Babbitt 
Metal- 


'•Edges  Chamfered 
Afterward 

FIG.  466. — Cutting  an  oil  groove. 


High  Spot  Being  Scraped 
From  Babbit 

FIG.  467. — Illustrating  method  of  scraping 
high  spots  from  a  bearing  quarter. 


Adjusting  Screw 


410.  Bearings  Are  Usually  Adjusted  To  Compensate  For 
Wear  By  Means  Of  Wedge  Blocks  And  Shims. — Main  and 
crank-pin  bearings  having  wedge  adjustments  are  shown  in 
Figs.  457  and  468.  In  the  main  bearing  (Fig.  457)  the  two 
side  boxes  are  so  adjusted  by  means  of  wedges,  (7,  that  the 
center  of  the  shaft  is  kept  over  the  reference  line,  J5.  The 

connecting-rod  crank-pin  bearing 
(Fig.  468)  is  adjusted  by  means  of 
the  cap  screws,  N.  These  move 
the  wedge,  W,  so  as  to  push  the 
end  brass,  B,  closer  to  the  station- 
ary brass,  D.  Shims  are  some- 
times used  between  the  two  brasses 
at  V.  Then  to  tighten  the  bear- 
ing, a  thin  shim  is  withdrawn 
and  the  wedge  set  tightly  against 
the  brass.  The  thickness  of  the 

shims  -should  be  such  that  a  good  running  fit  is  secured 
between  the  bushing  and  the  crank  pin.  If  no  shims  are 
used,  the  wedge  must  not  be  set  tightly  against  the  brass  or 


Shims*        C      C 

FIG.  468. — Crank-pin  bearing  with 
wedge  and  shims  for  adjustment. 


SEC.  410]    RECIPROCATING-ENGINE  MANAGEMENT 


401 


Brasses  In      ,  Play  Around  Crank 


the  crank  pin  will  be  clamped  and  will  not  turn  freely.  If 
there  is  much  wear,  a  shim,  S,  should  be  inserted  behind  the 
stationary  bushing.  If  this  is  not  done,  the  effective  length 
of  the  rod  will  be  decreased  due  to  the  wear  in  the  stationary 
bushing.  This  will  have  the 
effect  of  increasing  the  clearance 
at  one  end  of  the  cylinder  and 
decreasing  it  at  the  other. 
Finally,  if  after  repeated  ad- 
justments the  two  brasses  come 
together  at  V  and  still  leave  too 
much  play  around  the  crank  pin 
(see  Fig.  469),  then  the  bearing 
is  said  to  be  " brass  and  brass.7' 
The  edges  of  the  brasses  must 
then  be  filed  or  planed  off  on  a  shaper  or  planer  so  as  to  per- 
mit further  adjustment.  A  crosshead  is  adjusted  as  explained 
under  Fig.  470.  The  wrist-pin  bearing  is  adjusted  exactly 
as  explained  for  crank-pin  bearings  since  these  two  bearings 
are  usually  similar  in  construction. 


A&ustirg  flfcg*.7  ILJj 


FIG  .  469. — Showing  bearing  "brass  and 
brass"  with  too  much  play. 


lhc//neef  S/Afe-. 


Wrist 
P/n 


FIG.  470. — Illustrating  method  of  adjusting  crosshead  shoes.  To  take  up  wear  in 
the  lower  shoe,  S,  (which  wears  faster  than  the  upper  one)  slack  off  on  nuts,  A,  and 
tighten  nuts  B.  When  the  adjustment  is  completed,  the  distances,  X  and  Y,  should  be 
equal,  unless  the  guide  itself  is  worn. 

NOTE.— SIMPLE  SPLIT  BEARINGS  (Fig.  427)  are  often  adjusted  by 
removing  a  shim  or  substituting  a  thinner  one  and  reclamping  the 
halves  of  the  bearing  tightly  together.  The  upper  half  may  require 
scraping  (Sec.  409)  to  insure  a  good  fit. 

26 


402    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 


Tin 
Liners- 


Handle 


NOTE. — THE  PROPER  AMOUNT  OF  CLEARANCE  BETWEEN  A  JOURNAL 
AND  ITS  BEARING  is  about  0.001  in.  for  each  inch  of  diameter  for  very 
accurately  machined  or  ground  parts  such  as  motor  spindles.  For 
ordinary  engine  bearings,  about  0.0015  in.  for  each  inch  of  diameter 
is  allowed.  In  taking  up  engine  bearings  for  wear,  it  is  usually  imprac- 
tical to  measure  the  clearance.  Therefore  the  bearings  are  often  adjusted 
by  removing  shims  until  the  journal  will,  when  the  bolts  are  tightened,  be 
gripped;  and  then  adding  sheets  of  paper  about  as  thick  as  the  clearance 
desired  until  it  will  again  turn.  A  very  slight  knock  is  preferable  to 
excessive  tightness  in  the  bearing.  A  bearing  which  is  too  tight  will 
heat  and  seize. 

411.  The  Principal  Causes  Of  Bearing  Heating  are:  (1) 
Not  enough  oil.  (2)  Bearing  too  tight.  (3)  Improper  oil. 
(4)  Grit  in  bearing.  (5)  External  heat.  (6)  Improper  design. 
(7)  Bearing  does  not  fit.  In  old  bearings,  heating  may  be 

due  to  warping  of  the  engine 
frame  or  warping  of  the  brasses, 
but  heating  is  more  common  with 
new  or  newly  fitted  bearings. 
The  remedies  for  the  above 
troubles  follow  naturally  from 
their  causes.  Failure  of  oil  may 
be  due  to  clogged  oil  holes  or 
pipes  or  the  oil  grooves  in  the 
bearing  face  may  be  clogged  or 
worn  off.  Too  thin  an  oil  will 
cause  a  bearing  to  heat;  see 
Sec.  476.  If  a  source  of  ex- 
ternal heat  cannot  be  removed, 
a  high-temperature  machine  oil 

FIG.  471.— An  improvised  device  for  Or  Cylinder  oil  must  be  USed. 
truing  up  crank  pins  without  removing  jf  ft  kearing  nag  begun  to  Cut 

due  to  grit  or  a  misfit,  it  should 

be  taken  apart  and  cleaned  and  scraped  (Sec.  409).  If  it  is 
loosened,  flooded  with  oil  and  then  turned  over  slowly  for  a 
time,  it  may  run  smooth  again. 

NOTE. — AN  IMPROVISED  DEVICE  FOR  SCRAPING  AND  TRUING  UP  A 
CRANK  PIN  is  shown  in  Fig.  471.  The  stones  are  set  opposite  the  highest 
spots  on  the  pin  and  the  device  is  rocked  back  and  forth  to  reduce  them, 
plenty  of  oil  being  used.  Tin  liners  are  removed  and  the  grinding 


SEC.  412]    RECIPROCATING-ENGINE  MANAGEMENT  403 

continued  until  the  stones  touch  evenly  when  the  device  may  be  revolved 
completely  about  the  pin. 

412.  If  A  Wrist-Pin  Or  Crank-Pin  Bearing  Starts  To  Heat, 
the  oil  supply  should  be  increased  and  a  heavier  oil  run  in. 
There  is  little  else  to  be  done  to  such  bearings  until  the  engine 
can  be  stopped.     Then  bearings  which  have  heated  should  be 
taken  apart  and  examined  for  the  cause.     If  the  brasses  are 
badly  warped  or  grooved,  they  should  be  refinished  or  replaced. 
Wires  should  be  run  into  the  oil  holes  to  make  sure  they  are 
clear.     The  new  or  newly  finished  brasses  should  be  left  a 
little  loose  at  first  to  avoid  a  repetition  of  the  trouble.     The 
inner  edges  (V,  Fig.  468)  should  be  rounded  or  recessed  to 
prevent  them  from  scraping  the  pin. 

413.  If  A  Main  Bearing  Starts  To  Heat  it  should  immedi- 
ately be  loosened  and  flooded  with  oil.     If  the  heating  con- 
tinues, a  mixture  of  cylinder  oil  and  graphite  may  be  worked 
into  it  in  any  convenient  way.     A  mixture  of  oil  and  powdered 
talc  or  soapstone  may  also  be  used  but  the  engine  should  be 
slowed  down  if  possible  when  such  mixtures  are  used.     Water 
may  be  used  on  the  shaft  to  keep  it  cool  but  if  there  is  any 
grit  in  the  water  it  should  not  be  allowed  to  run  into  the  oil 
passages  or  get  between  the  rubbing  faces.     It  is  not  advisable 
to  apply  water  to  the  outside  of  the  bearing  box  as  this  may 
cause  the  bearing  to  seize. 

414.  If  A  Main  Bearing  Becomes  So  Hot  That  It  Burns 
The  Hand  Or  Smokes,  the  engine  must  be  slowed  down 
immediately  or  the  bearings  will  be  melted  out.     Then  with 
the  engine  turning  over  slowly,  loosen  the  bearing  slightly  and 
work  cylinder  oil  into  the  bearing.     One  of  the  above  oil 
mixtures  should  then  be  worked  into  the  bearing.     Water 
should  be  used  cautiously  on  a  very  hot  bearing  or  shaft  to 
avoid  cracking  and   warping.     After  the  bearing  has  cooled 
somewhat  and  is  well  oiled  the  engine  may  be  stopped.     The 
bearing  must  then  be  repaired  according  to  the  extent  of  the 
damage — scraped,  refinished  or  re-babbitted. 

415.  Packings    For    Steam   Engines    should   be    carefully 
selected  and  kept  on  hand.     For  packing  piston  rods,  soft 
fiber  packing,  flexible  metallic  packing  and  regular  metallic 
packing  are  used.     Soft  packing  should  be  used  only  where 


404    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE   [Div.   13 


Layers  Of  Fabric 

And  Rubber  Compounds.. 


low  first  cost  is  essential  or  where  the  rod  is  so  badly  scored 
that  a  metallic  packing  cannot  be  utilized.  Soft  packing  is 
preferably  ordered  in  rings  (Fig.  472)  which  should  fit  neatly 
around  the  rod.  But  it  may  be  ordered  in  coils  and  afterward 
cut  into  rings.  For  stuffing  boxes  over  %  in.  in  width  between 
the  rod  and  the  wall,  the  soft  packing  should  be  ordered  to  fit 
the  box.  Smaller  sizes  may  be  ordered  to  fit  also  but  small 
boxes  are  usually  packed  with  twisted  or  braided  coil  packing 

which  is  fed  into  the  box  so  as 
to  form  a  loose  spiral.  In  gen- 
eral, soft  packings  in  which 
rubber  is  in  direct  contact  with 
the  rod  should  be  avoided.  In 
general,  metallic  packings  are 
more  economical  and  satisfac- 
tory in  the  long  run,  than  are 
soft  packings.  Flexible  metallic 
packing  is  used  just  as  is  soft 
fiber  packing  and  can  be  used 
on  slightly  scored  rods  and  for 
superheated  steam.  It  is  cheaper 
than  regular  metallic  packing 
but  it  will  not  last  as  long  and 
produces  more  friction.  Regular 
metallic  packing  (Fig.  369),  aside  from  its  high  first  cost, 
has  decided  advantages  when  applied  to  new  or  unscored 
rods;  regular  metallic  packings  will  usually  last  as  long  as  the 
engine,  can  be  used  with  highly  superheated  steam,  have 
little  friction  and  do  not  absorb  water.  A  water-saturated 
packing  will  corrode  the  rod.  In  ordering  regular  metallic 
packing,  a  sketch  giving  the  shape  and  all  interior  dimensions 
of  the  stuffing  box  and  the  rod  diameter  should  be  sent  with 
the  order.  For  the  water  ends  of  pumps,  flax  or  hemp  packings 
are  usually  used  but  various  metallic  packings  are  recommended 
by  their  makers  and  are  probably  more  economical  for  this 
service. 

NOTE. — SHEET  PACKING  for  valve-chest  covers  and  flanged  joints 
is  usually  about  ^2  to  %  in.  thick.  For  temperatures  below  about 
300  deg.  fahr.,  rubber  composition  sheet  packing  is  widely  used.  Cor- 
rugated copper  gaskets  or  sheet  asbestos  packing  may  also  be  used  for 


I- Square  Section  Rubber    ^ 
'  Core 


E-  Round   Section 
FIG.  472. — Square  and  round-section 
soft  ring-packing. 


SEC.  416]    RECIPROCATING-ENGINE  MANAGEMENT 


405 


this  service.  For  higher  temperatures,  copper  or  asbestos  gaskets 
should  be  used.  A  gasket  of  copper  with  asbestos  inserts  is  used  for 
very  high  temperatures  and  pressures  but  is  too  expensive  and  unnec- 
essary for  common  service. 

NOTE. — SOFT  PACKING  MUST  USUALLY  BE  REPLACED  EVERY  FEW 
MONTHS.  To  replace  the  packing,  simply  unscrew  the  gland  nuts, 
slide  the  gland  along  the  rod,  and  pull  out  the  old  rings  with  a  packing 
hook.  The  new  rings  should  fit  neatly,  as  in  Fig.  473-77,  and  should  be 
coated  with  graphite  and  oil  before  they  are  inserted.  The  joints  of  the 
different  rings  should  alternate  on  opposite  sides  of  the  rod.  The 
gland  should  be  tightened  only  enough  to  prevent  any  considerable 
leakage.  With  a  very  good  fit,  the  nuts  need  be  only  hand  tight.  Be 
careful  in  tightening  valve-stem  glands  on  automatic  engines  so  as  not 
to  introduce  much  friction;  otherwise  the  governor  action  will  be  hindered. 
It  is  a  good  plan  to  first  apply  a  considerable  pressure  on  the  gland  to 


Stuffing 


.- Round  Sect  ion 
Soft  Packing 

.•Gland 


Ftickingr  Rings 


Mncorrect  ^^         I- Correct 

FIG.  473. — Showing  incorrect  and  correct  arrangements  of  packing  in  stuffing  box. 

force  the  packing  firmly  into  place.  The  gland  nuts  should  then  be 
slacked  off  somewhat.  For  small  rods,  the  procedure  is  the  same  except 
that  it  is  not  necessary  to  have  the  packing  in  rings.  Twisted  or  braided 
coil  packing  may  be  fed  into  the  stuffing-box  so  as  to  lie  neatly  in  spiral 
form. 

416.  If  An  Engine  Gets  Out  Of  Line,  some  of  the  bearings 
are  likely  to  be  cramped  or  caused  to  knock.  By  getting  out 
of  line  is  meant  shifting  of  some  essential  part  of  the  engine 
so  that  it  is  in  the  wrong  position  with  respect  to  the  rest  of 
it.  For  instance,  one  crank-shaft  bearing  may  be  higher  than 
the  other  due  to  settling  of  the  outboard  bearing  foundation. 
Settling  of  the  guide  pedestal  (Fig.  474)  has,  in  some 
instances,  caused  knocks.  Warping  of  the  frame  or  other 
parts  or  incorrect  adjustment  of  the  main  bearings  may  also 
throw  the  engine  out  of  line. 


406     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE   [Div.  13 


NOTE. — FOR  AN  ENGINE  To  BE  IN  LINE,  the  following  conditions 
should  obtain:  (1)  The  axial  center  line  of  the  shaft  and  its  bearings 
should  be  level  and  should  intersect  the  axial  center  line  of  the  cylinder  at 
right  angles.  (2)  The  guides  should  be  parallel  to  each  other  and  to  the 


Frame  -- 


FIG.  474. — Showing  settling  pedestal  which  caused  the  engine  to  settle  out  of  line  and 

knock. 

axial  center  line  of  the  cylinder.  (3)  The  wrist  pin  and  crank  pin  and 
their  bearings  should  be  parallel  and  parallel  to  the  shaft.  (4)  In  most 
engines,  the  stuffing  box  and  piston  rod  should  be  concentric  with  the  cylinder 
and  the  guides  equidistant  from  the  center  line  of  the  cylinder.  (5)  The 


a-  -u 


Generator*  ^   ^  :  ,  — £ 

SID 


Outboard 
Bearinq- 


FIG.  475 — Plan  lay-out  of  direct-connected  simple  engine  with  outboard  bearing. 

center,  E  (Fig.  475),  of  the  crank-pin  journal  should  lie  in  the  vertical 
plane  of  the  cylinder  axis,  for  all  positions  of  the  crank  pin. 

NOTE. — THE   ORDER   IN   WHICH   THE   VARIOUS   ALIGNMENTS   ARE 
MADE    OR    CHECKED    is   important.     If  it  is  suspected  that  several 


SEC.  416    RECIPROCATING-ENGINE  MANAGEMENT 


407 


alignments  (Fig.  475)  are  "off,"  the  order  in  which  they  should  be 
corrected  is  as  follows  (1)  For  a  horizontal  engine,  level  the  cylinder;  for 
a  vertical  engine  plumb  the  cylinder.  (2)  Stretch  the  center  line  of  the 
cylinder.  (3)  Stretch  the  center  line  of  the  shaft.  (4)  Square  shaft 
center  line  with  cylinder.  (5)  Level  center  line  of  shaft.  (6)  Test  align- 
ment of  guides.  (7)  Test  alignment  of  crosshead  and  wrist  pin.  (8)  Test 
alignment  of  crank  pin.  (9)  Test  alignment  of  connecting  rod  brasses. 


o  / 


.Shaft-Axis  Center-Line  Wire 


Cylinder- Axis 
Center- Line  Wire. 


.  Bed  Plate- 

'•Wooden  Board 

FIG.  476. — Center-line  wires  in  position  for  aligning  an  engine. 


EXPLANATION. — The  following  method  of  aligning  an  engine  is  adapted 
for  use  in  erection  and  in  re-assembling  during  overhauling.  Fig.  475 
shows  a  plan  view  of  a  simple  engine  direct  connected  to  a  generator. 
Assume  that  the  main  moving  parts,  namely  the  piston  and  rod,  the 
crosshead  and  connecting  rod,  crank  shaft  and  generator  armature  are 
all  removed.  Bolt  a  board,  A  (Figs.  475  and  476),  across  the  end  of  the 
cylinder  between  two  cylinder-head  studs  and  stretch  a  fine  steel 
("piano  ")  wire  or  a  strong  small-diameter  "fish  line, "  AB,  between  A  and 
an  improvised  wooden  block  or  batter  board,  B.  The  wire,  which  should 
be  about  ^4  in.  in  diameter,  is  care- 
fully located  in  the  center  of  the  cylin- 
der at  A  by  means  of  a  pair  of  dividers 
or  inside  calipers.  The  location  of 
the  other  end  is  found  by  trial  so  that 
the  wire  passes  through  the  center  of 
the  cylinder  stuffing  box  (Fig.  477)  as 
determined  by  using  a  pair  of  inside 
calipers  around  the  wire.  Then  the 
wire,  CD,  is  stretched  so  that  it  is 
level,  passes  through  the  axis  of  FIG.  477.— Method  of  locating  center- 
the  main  bearing,  F,  and  is  at  right  lin°  ™  in  ^  cfnter  of  "  e^? 

,     stuffing  box.     The  distance,  AB,  should 
angles     to     AB.      A     spirit-level     and     be  the  same  in  every  direction. 

carpenter's   square   may  be  used  for 

this  operation  or  a  triangular  wooden  templet  may  be  laid  off  for  squaring 
the  wires  for  large  engines.  A  triangle  with  sides  of  8  by  6  by  10  ft. 
will  have  a  square  corner.  If  CD  passes  below  AB,  a  liner  should  be 
inserted  under  the  bearing  to  lift  the  bearing  into  place.  If  the  outboard 


1^.  -  -Wire  Representing 
Cylinder  Ax/a/ 
Center  Line 


408    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 

bearing  is  found  to  be  out  of  place  with  respect  to  CD,  it  should  be 
shifted  or  shimmed  into  place.  If,  the  shaft  having  been  squared  with 
the  cylinder  axis,  the  center,  E,  of  the  crank-pin  journal  does  not  fall  on 
the  axial  center  line  of  the  cylinder  as  shown,  it  usually  means  that  the 
shaft  collar  or  eccentric  has  slipped  longitudinally  on  the  shaft. 

417.  An  Engine  May  Be  Lined  Up  Without  Removing  The 
Moving  Parts  by  a  method  shown  in  Fig.  478.     This  method 


-  Measuring 

From  Connecting    Rod 


![•  Measuring   From 

Center  Of  Cylinder 


I -General  View 


Fia.  478. — Showing  quick  method  of  checking  engine  alignment.     (Southern  Engineer 

Kink  Book.) 

is  adapted  for  use  when  locating  trouble  and  at  other  times 
when  it  is  inconvenient  to  dismantle  the  moving  parts  of  the 
engine. 


SEC.  418]    RECIPROCATING-ENGINE  MANAGEMENT  409 

EXPLANATION. — A  board,  GQ  (Fig.  478),  is  bolted  across  the  end  of  the 
cylinder  between  two  cylinder-head  studs  so  that  it  extends  beyond  the 
engine  frame.  The  center  of  the  cylinder  is  located  on  the  board  at  C 
by  means  of  a  pair  of  dividers  or  inside  calipers.  The  point  Q  is  located 
level  with  C.  A  wire,  QR,  is  stretched  level  as  shown  and  as  nearly 
parallel  with  the  cylinder  axis  as  it  can  be  aligned  with  the  eye.  Make 
a  gage,  A,  by  driving  a  pin  or  brad  into  the  end  of  a  stick  of  wood. 
Scratch  a  line,  M,  on  A  so  that  M  falls 
on  C  when  A  is  held  to  the  line  as 


shown  in  II.     Also  make  a  gage,  B, 


--  --X." 


having  a  pin   or  brad  in  each  end. 

Make  B  shorter  than  A  by  a  distance 

which  is  equal  to  the  radius  of  the  *• -Unequal  \£>;stances~.._ 

piston  rod.     With  the  engine  on  ap-  V  Line  p»ra/iei  TO  Axis-* 

proximate     crank-end    dead    center  ^    479.-Showing  how  incorrect 

apply  gage  B  between  the  piston  rod  shaft  aiignment  may  be  detected  at 

and    the    wire    line    near   the    Stuffing     dead  centers  by  measuring  from  a  line 
box     as    Shown    in     ///.       Move     the     which  is  Parallel  to  the  cylinder  center 

end,   R,  of  the  line,  L,  horizontally    hne* 

so  that  B  will  just  touch  the  rod  and  line  as  shown.     The  wire  line  should 

now  be  parallel  to  the  cylinder  axis. 

The  gage,  B,  is  then  applied  to  the  rod  near  the  crosshead.  If  the 
guides  are  in  line,  the  distance  will  be  the  same  as  at  the  stuffing-box. 
Ordinarily  the  proper  location  for  the  line  may  be  located  by  measuring 
from  the  rod  only  near  the  crosshead  because  the  guides  are  seldom  out 
of  line;  but  it  is  well  to  check  this  condition  by  a  measurement  near  the 
stuffing-box.  The  gage,  A,  is  now  applied  to  the  connecting  rod,  measur- 
ing to  a  scribed  line,  H,  above  the  center  of  the  crank-pin  bearing.  Mark 
the  position  of  H  on  the  gage,  turn  over  to  head-end  dead  center  and 
mark  the  position  of  H  again  in  the  same  way.  If  H  falls  first  on  one 
side  of  M  and  then  on  the  other,  or  is  at  a  different  distance  from  M 
at  the  two  dead-center  positions,  the  outboard  bearing  should  be  shifted 
to  bring  the  shaft  into  line.  How  the  difference  in  distance  from  the 
line  shows  an  incorrect  shaft  alignment  may  be  understood  from  Fig. 
479.  If  there  is  a  considerable  constant  difference  between  H  and  M, 
the  crank  pin  is  out  of  line  due  to  the  shaft  slipping  longitudinally. 

418.  The  Normal  Wear  Of  The  Main  Bearing  May  Cause 
The  Shaft  To  Get  Out  Of  Line. — As  the  bearing  wears,  the 
shaft  sinks  continually  lower  at  the  crank  end.  The  amount 
of  this  wear  may  be  measured  by  means  of  a  tram  or  trammel 
gage,  G  (Fig.  480) .  A  center-punch  mark  is  made  on  the  base 
plate  of  the  engine  or  the  bottom  of  the  crank  pin  and  the  long 
end  of  the  gage  inserted  therein.  The  gage  should  be  of  such 
a  length  that  the  short  end  will  fall  in  the  center  of  the  shaft 


410    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 

when  the  shaft  position  is  correct.  The  amount  of  movement 
from  this  position  may  then  be  readily  detected.  When  the 
shaft  gets  considerably  lower  .than  its  correct  position,  it  may 
be  restored  by  jacking  up  and  inserting  a  liner  under  the 
lower  shell  of  the  bearing. 


Engine 
FIG.  480. — Showing  a  method  of  gaging  the  wear  of  a  main  bearing. 

419.  A  Table  Describing  The  Principal  Causes  Of  Engine 
Knocks  And  Their  Remedies  is  given  on  the  opposite  page. 


CAUTION. — Do  NOT  TIGHTEN  ANY  BEARING  To  STOP  A  KNOCK 
UNLESS  IT  Is  KNOWN  THAT  THE  PARTICULAR  BEARING  Is  LOOSE  and 
is  causing  the  knock.  If  a  bearing  which  is  already  in  good  condition 
is  tightened  to  stop  a  knock  which  is  caused  by  something  else,  the  bearing 
will  be  likely  to  heat  and  will  have  to  be  carefully  readjusted.  If  a  certain 
bearing  is  thought  to  be  the  cause  of  the  knock  but  there  is  some  uncer- 
tainty, tightening  the  bearing  may  be  tried  but  the  original  position  of 
the  bolts  should  be  carefully  noted;  and,  if  the  tightening  does  not 
diminish  the  knock,  the  original  condition  should  be  restored. 

NOTE. — THE  APPARENT  LOCATION  OF  A  KNOCK  Is  OFTEN  DECEPTIVE 
due  to  the  fact  that  the  sound  travels  along  the  engine  frame.  It 
requires  experience  to  locate  a.  knock  with  any  certainty.  Nearly  all 
knocks  occur  at  the  ends  of  the  stroke,  bearing  knocks  occurring  just  as 
the  direction  is  reversed  at  each  end.  Cylinder  knocks  due  to  water 
or  deposits  in  the  cylinder  are  more  likely  to  occur  at  one  end  only.  A 
violent  knock  just  after  an  adjustment  may  be  due  to  interference  such 
as  the  piston  striking  the  cylinder  head  after  a  careless  connecting-rod 
bearing  adjustment. 

NOTE. — BY  FAR  THE  COMMONEST  CAUSES  OF  KNOCKS  ARE  WATER 
IN  THE  CYLINDER  AND  LOOSE  BEARINGS.  Remedies  for  these  should 
therefore  be  tried  first  unless  the  cause  is  known  to  be  some  other.  If 
the  knock  persists  after  this,  the  other  remedies  should  be  tried  in  order 
of  their  probability  somewhat  as  given  in  the  table. 


SEC.  419]    RECIPROCATING-ENGINE  MANAGEMENT 


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412    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 


.-Dash- Pot  Rod 
From  Valve  Arm 


420.  The  Location  Of  A  Knock  Can  Often  Be  Ascertained 
By  Means  Of  a  Sounding  Rod. — Any  light  metal  rod  which  is 
about  2  or  3  ft.  long  and  which  has  one  reasonably  smooth 
end  may  be  used  as  a  sounding  rod.     One  end  is  placed  against 
the  stationary  part  of  the  engine  where  the  knock  is  suspec- 
ted.    The  smooth  end  is  placed  against  the  side  of  the  opera- 
tor's face  near  his  ear.     Try  several  locations  in  this  way. 
Where  the  sound  is  greatest,  the  knock  is  probably  located. 
A  wooden  rod  may  be  used  but  is  not  quite  as  good. 

421.  When    An   Engine  Runs  "Under"  (Sec.  32),  knocks 
are   likely  to   occur  in   the  guides.     It  may  be   noted  (see 
Fig.  20)  that  when  an  engine  runs  "  under,"  the  thrust  on  the 
connecting  rod  tends  to  lift  the  crosshead  except  at  dead 
centers.     Therefore  the  crosshead  will  ride  against  the  upper 

guide  during  the  stroke  and 
against  the  lower  one  at  dead 
centers.  If  there  is  any  play  be- 
tween the  crosshead  and  the 
guides,  the  crosshead  will  strike 
the  upper  guide  and  fall  to  the 
lower  guide  at  the  end  of  each 
stroke,  thus  causing  a  knock. 
When  the  engine  runs  "over" 
the  crosshead  always  rides  on  the 
lower  guide.  Engines  are  more 
often  run  "  over"  for  this  reason. 
422.  Troubles  Of  Dash-Pots 
For  Corliss  Releasing  Gears 
are,  principally,  as  follows:  In 
some  designs  the  vacuum  created 
by  the  lifting  of  the  plunger,  L 
(Fig.  481),  is  relied  on  to  return  the  pot  to  its  closed  position. 
The  vacuum  cylinder  may  be  packed  with  cup  washers  or 
packing  rings,  P,  which  must  be  in  good  condition  to  maintain 
the  necessary  vacuum.  Failure  of  the  vacuum  will  prevent 
the  admission  valves  from  closing  rapidly.  A  spring  may  be 
used  temporarily  when  this  occurs.  If  the  valve,  V,  through 
which  the  air  is  released  from  the  cushion  space  is  open  too 
wide,  the  dash-pot  will  slam.  If  it  is  not  open  wide  enough, 
the  dash-pot  is  likely  to  bounce  or  not  return  to  rest  in  time 


FIG.  481. — Showing  inverted  vacuum 
dash-pot  for  Corliss  valve  gear. 


SEC.  423]    RECIPROCATING-ENGINE  MANAGEMENT  413 

for  the  next  stroke.     Also  it  may  not  allow  the  valves  to  shut 
off  completely. 

423.  The  Following  Information  Concerning  Each  Engine 
Should  Be  Ascertained  and  kept  for  ready  reference  so  that 
repair  parts  may  be  ordered  promptly.  A  copy  of  this  form, 
properly  filled  in,  should  be  framed  under  glass  and  mounted 
near  each  engine. 

DATA  FORM — ENGINE 

Date  when  made  up 

Engine  No Maker 

Type Age 

Kind  of  engine 

No.  of  cylinders Diam Length 

Thickness Cylinder  head  thickness 

Cylinder  head  bolts,  No Size 

How  is  cylinder  supported 

Piston,  type Area 

Thickness Construction , 

Rings,  No Width Diam 

Piston  rod  diam Length Taper 

Thread  on  end  of  rod  at  piston Crosshead 

Follower  bolts,  No Size 

Crosshead  type 

Length Height Width 

Wrist  pin,  diam Length 

Shoes,  length Thickness Material 

Method  of  attaching  wrist  pin 

Connecting  rod,  type 

Length Diam.  min Max 

Box  adjustment 

Wedge  bolts,  No Size 

Crank,  type Throw 

Crank  pin  diam Length 

Eccentric  rod  diam Length 

Eccentric  throw 

Rocker  arms,  type 

Length Travel Pin  sizes 

Bearings,  type Length 

Material  in  boxes 

Adjustment 

Governor  type R.p.m 

How  driven 

What  does  governor  act  upon 

Engine  r.p.m Steam  pressure 

Foundation  material Floor  area 

What  does  engine  drive 


414    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.'lS 


SEC.  424]    RECIPROCATING-ENGINE  MANAGEMENT  415 

424.  Careful  Records  Should  Be  Kept  of  engine  performance 
and  other  events  in  the  engine  room.  These  records  will 
enable  the  plant  manager  to  determine  the  effect  of  changes 
which  he  may  make  in  the  methods  of  operation  and  will 
show  in  what  ways  improvements  in  management  may  be 
made.  The  form  shown  in  Fig.  482  may  be  found  useful  in 
keeping  such  records. 

QUESTIONS  ON  DIVISION  13 

1.  Name  three  precautions  to  be  taken  in  replacing  a  cylinder  head.     How  may  piston 
leakage  be  judged? 

2.  Name  three  conditions  which  should  obtain  in  a  valve  chest  before  the  cover  is 
replaced. 

3.  What,  in  general,  should  be  done  by  an  engineer  in  taking  charge  of  an  engine  room 
with  which  he  is  not  familiar? 

4.  Name  some  points  which  should  be  noted  in  inspecting  condensers? 

5.  Give  two  suggestions  to  aid  in  remembering  power  plant  piping  connections. 

6.  What   conditions   of  steam   and   water   piping   arising   from   neglect   should    be 
corrected? 

7.  How  may  traps  and  water  gages  be  inspected? 

8.  Name  a  few  supplies  which  should  be  kept  on  hand  in  an  engine  room. 

9.  Make  a  sketch  of  piping  used  in  warming  up  a  simple  engine  and  explain  its  use. 

10.  When  should  gravity-feed  bearing  lubricators  be  started?     Cylinder  lubricators? 

11.  Should  the  condenser  be  started  before  or  after  starting  a  condensing  engine? 
Why? 

12.  After  starting  an  engine  when  may  its  drain  valves  be  closed? 

13.  How  is  steam  worked  into  both  ends  of  a  slide-valve  engine  which  is  not  provided 
with  by-pass  piping?     How  into  the  low-pressure  cylinder  of  a  compound  engine? 

14.  In  stopping  the  condensing  engine,  when  should  the  wet-air  pump  of  a  low-level 
jet  condenser  be  stopped? 

15.  What  is  the  chief  source  of  trouble  in  condenser  operation?     How  may  it  be 
located? 

16.  Explain  how  to  change  from  non-condensing  to  condensing  operation. 

17.  What  may  cause  a  condenser  to  fail  and  the  engine  to  exhaust  through  the  relief 
valve? 

18.  What  is  the  purpose  of  a  governor  starting  cam  on  a  detaching  Corliss  engine? 
A  starting  lever?     A  reach-rod  latch? 

19.  How  can  a  detaching  Corliss  engine  be  started  when  the  governor  is  in  "safety 
position"? 

20.  What  difference  is  there  in  the  starting  of  a  cross-  and  a  tandem-compound  engine? 

21.  What  is  the  danger  in  using  emery  powder  in  cleaning  the  polished  surfaces  on  an 
engine?     What  is  the  preferable  method  of  cleaning  polished  work? 

22.  How  may  a  solid  snap  piston  ring  be  removed?     How  may  the  fit  of  a  worn  snap 
ring  be  restored? 

23.  Explain  a  method  of  truing  up  a  filed  piston  ring  by  using  a  surface  plate.     Explain 
how  the  fit  of  a  ring  in  a  cylinder  may  be  tested. 

24.  May  a  good  bearing  be  ordinarily  made  by  pouring  babbitt  around  a  shaft  and 
leaving  the  bearing  surface  as  it  forms?     Why?     How  should  oil  be  distributed  over  the 
face  of  a  bearing?     Explain  with  sketches. 

25.  What  is  the  purpose  of  a  mandrel  which  is  used  in  babbitting  a  bearing?     How 
may  one  be  made?     In  what  position  is  a  main  bearing  preferably  babbitted?     Why? 

26.  What  is  the  danger  of  repeatedly  taking  up  crank-pin  bearing  wear  by  moving  only 
one  brass? 


416    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE   [Div.  13 

27.  What  should  be  done  when  a  crank-pin  bearing  is  "  brass  and  brass  "  and  is  still  too 
loose? 

28.  How  are  simple  split  bearings  adjusted?     What  clearance  should  there  ordinarily 
be  between  an  engine  journal  and  its  bearing? 

29.  Name  six  conditions  which  will  cause  bearings  to  heat. 

30.  What  can  be  done  to  stop  the  heating  of  a  crank-pin  bearing  without  stopping  the 
engine? 

31.  What  should  be  done  when  a  main  bearing  starts  to  heat? 

32.  Give  general  directions  for  handling  a  badly  overheated  main  bearing. 

33.  What  are  some  advantages  of  metallic  packing  on  good  rods? 

34.  How  should  metallic  packing  be  ordered?     How  soft  packing  over  %  in.  wide? 

35.  What  are  possible  causes  of  an  engine  getting  out  of  line?     What  are  the  results? 

36.  In  what  order  should  the  various  alignments  of  an  engine  be  made  in  erecting? 
Explain  the  procedure  using  a  sketch. 

37.  If,  when  erecting  an  engine,  the  correct  axial  center  line  for  the  shaft  is  found  not  to 
pass  through  the  center  of  the  outboard  bearing,  what  should  be  done? 

38.  How  may  the  alignment  of  an  engine  be  tested  without  dismantling  it?     Explain 
with  a  sketch  what  is  indicated  if  the  crank  pin  is  a  different  distance  at  the  two  dead 
centers  from  a  reference  line  which  is  level  and  which  is  parallel  with  the  cylinder  axis. 

39.  Name  six  causes  of  engine  knocks  and  their  remedies.     Which  are  the  most 
common? 

40.  What  danger  lies  in  tightening  bearings  to  stop  any  knock  which  occurs  in  an 
engine? 

41.  Why  are  engines  usually  run  "over"? 

42.  What  happens  if  the  plunger  in  the  dash-pot  of  a  Corliss  valve  gear  leaks  exces- 
sively?    What  if  the  cushion  air  escapes  too  rapidly?     What  if  it  escapes  too  slowly? 

43.  Why  should  engine  room  records  be  kept? 

44.  Explain  a  method  of  repairing  a  plain  D-slide  valve  without  machine  tools.     How 
are  piston  valves  repaired  when  the  leakage  is  found  to  be  excessive?     Corliss  valves? 


DIVISION    14 
USE  OF  SUPERHEATED  STEAM  IN  ENGINES 

425.  The  Use  Of  Superheated  Steam  In  Engines  Always 
Results  In  Some  Gain. — Actual  fuel  savings,  due  to  super- 
heating an  engine's  steam  supply,  range  from  6  to  20 
per  cent.  Whether  the  expense  of  installing  and  maintaining 
the  superheater  (Figs.  483  and  484)  is  justified  can  be  deter- 

18Lb.Of  Steam  @  1103 B.TU. 'Per Lb.=19,854 B.J.U.  Per 
I      I.H.R:Hr.,  Delivered  By  Boiler  To  Engine 


1-14,668  B.T.U. 
''.Absorbed  By 
'Condenser 


,•  Superheater 

1,156  B.IU.  Per  Lb,\;_        Engine 


Heat 


I- Super  heated  Steam  Plant 


FIG.  483. — Diagram  showing  theoretical  heat  transfer  calculated  for  saturated  and 
superheated  steam  plants.  The  figures  are  based  on  one  indicated  horsepower  hour. 
Steam  pressure  =  105  per  sq.  in.  abs.  Superheat  =  100  deg.  fahr.  The  condenser 
temperature  =  116  deg.  fahr.  The  heats  are  calculated  above  this  temperature. 
A  typical  steam  saving  due  to  superheat  is  assumed. 

mined  only  by  comparing  such  expense  with  the  value  of  the 
fuel  saving  which  is  effected  by  superheating  the  steam.  This 
fuel  saving  in  simple  engines  is  about  1  per  cent,  for  each  10  deg. 
fahr.  of  superheat.  Whether  a  high  initial  steam  presssure 
with  slight  superheat  or  a  low  pressure  with  high  superheat 

27  417 


418     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  14 

is  the  more  economical  depends  on  the  type  and  other  operat- 
ing conditions  of  the  engine  (Sees.  432-435). 

NOTE. — FOR  DEFINITION  AND  THEORETICAL  DISCUSSION  OP  SUPER- 
HEATED STEAM,  see  the  author's  PRACTICAL  HEAT.  See  also  Div.  10. 
The  efficiency  of  the  ideal  Rankine  cycle  is  not  materially  increased  by 
moderate  superheat  (see  Sec.  315).  But  with  superheated  steam  there  is 
less  cylinder  condensation  and  less  pressure  drop  from  the  boiler  to  the 
engine  cylinder.  Hence,  while  the  use  of  superheated  steam  does  not 
materially  increase  the  Rankine- cycle  efficiency  it  does  increase  the 
thermal  efficiency  and  hence  the  Rankine-cycle  ratio. 


S  Superheated  Steam  To  Engine 


.---  Saturated  Steam  From  Boiler  -  -  - 


FIG.  484. — Typical  modern  superheater  installation.     (Superheater  installed  in. 
boiler  set  ting.) 

426.  The  Differences  Between  Superheated  And  Saturated 
Steam  at  the  same  pressure  may  be  enumerated  as  follows: 

1.  Superheated  steam  is  generated  first  as  saturated  or  wet  steam  and 
then  further  heated  in  a  superheater,  practically  no  water  being  present, 
and  is  thus  converted  into  superheated  steam.     That  is,  its  temperature 
is  raised  above  the  boiling  point  at  the  given  pressure. 

2.  The  temperature  of  superheated  steam  is  greater  at  the  same  pressure 
than  that  of  saturated  steam.     Saturated  steam  at  a  given  pressure  exists 
at  only  one  temperature — the  boiling  point  at  that  pressure;  but,  at 
this  same  pressure,  superheated  steam  may  have  any  temperature  above 
the  saturated  steam  temperature. 

3.  The  volume  of  superheated  steam  is  greater  than  that  of  the  same 
weight  of  saturated  steam  at  the  same  pressure,  that  is,  its  density  is  less. 
Steam,  in  being  superheated,  expands  so  that  its  volume  varies  roughly  as 
the  absolute  temperature.     The  exact  volume  which  it  occupies,  however, 


SEC.  427]        SUPERHEATED  STEAM  IN  ENGINES  419 

must  be  found  from  a  superheated-steam  table  or  chart.  Less  weight 
of  superheated  steam  is  therefore  required  to  fill  a  certain  volume  and 
thus  for  a  given  amount  of  work  by  an  engine.  This  lesser  weight  of 
steam  requires  a  lesser  condenser  and  air  pump  capacity;  or,  conversely, 
results  in  a  higher  vacuum  for  a  given  condenser  and  air'pump  capacity. 
4.  The  total  heat  per  pound  of  superheated  steam  is  (Fig.  483)  greater 
than  that  of  saturated  steam  at  the  same  pressure;  also  superheated  steam 
contains  more  heat  than  does  saturated  steam  at  the  same  temperature. 

.  5.  Superheated  steam  may  be  cooled  somewhat  without  condensation 
taking  place.  Any  abstraction  of  heat  from  saturated  steam  causes 
condensation  but  the  superheat  which  superheated  steam  contains,  in 
addition  to  the  heat  contained  in  saturated  steam  at  the  same  pressure, 
may  all  be  abstracted  from  superheated  steam  before  any  condensation 
occurs. 

6.  Superheated  steam,  so  experiments  tend  to  indicate,  decreases  more 
in  volume  for  a  given  abstraction  of  heat  than  does  saturated  steam.     This 
appears  to  be  the  cause  of  the  expansion  lines  of  indicator  diagrams, 
which  are  taken  while  using  superheated  steam,  to  fall  off  somewhat 
more  rapidly  than  they  would  were  saturated  steam  used  under  the 
same  conditions. 

7.  Superheated  steam,  if  brought  into  contact  with  a  small  amount  of 
water,  will  evaporate  all  or  part  of  the  water;  whereas  saturated  steam  will 
not  evaporate  any  water.     Therefore  superheated  steam  never  contains 
any  suspended  water  in  the  form  of  fine  droplets  nor  does  it  carry  any 
water  mechanically  as  does  wet  steam. 

8.  Superheated  steam  has   lower  heat  conductivity  than  has  saturated 
steam,  probably  because*  there  is  no  moisture  in  it.     Therefore  it  does 
not  lose  heat  through  the  walls  of  a  pipe  as  readily  as  does  saturated 
steam.     For  this  reason,   it  is  usually  more  economical  to  transmit 
superheated  steam  than  saturated  steam  at  the  same  pressure,  in  spite  of 
the  higher  temperature  of  the  superheated  steam. 

9.  Superheated  steam  has  less  viscosity  or  fluid  friction  than  has  saturated 
steam.     Hence,  there  is  less  loss  of  pressure  due  to  wire-drawing  in  engine 
valves  when  superheated  steam  is  used.     A  given  volume  of  superheated 
steam  will  ordinarily  flow  through  a  given  pipe  line  in  a  given  time  with 
less  loss  in  pressure  than  will  the  same  volume  of  saturated  steam. 
However,  because  of  the  lesser  density  of  the  superheated  steam,  the 
weight  of  superheated  steam  transmitted  at  a  given  pressure  through  a 
pipe  is  somewhat  less  than  if  the  steam  were  saturated. 

427.  Valves  For  Engines  Using  Highly  Superheated  Steam 

are  usually  of  the  piston  (Fig.  485)  or  poppet  (Fig.  486) 
types.  Locomotive  and  marine  engines  which  operate  on 
superheated  steam  usually  have  piston  valves.  Stationary 
engines  for  highly  superheated  steam  usually  have  poppet 
valves.  Simple  slide  valves  can  only  be  used  for  slightly 


420    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE   [Div.  14 


superheated  steam  because  of  their  tendency  to  warp  when 
exposed  to  the  hot  dry  vapor.     The  maximum  amount  of 


, 

Exhaust 
5team^ 


Inside  admission     Exhaust 


*  Packing  Gland  "  Piston' 
I  FIG.  485. — Section  through  cylinder  of  Erie-Ball  piston-valve  engine. 


Auxiliary  Exhaust-} 
Valve  Cam- ' 


Single-Beat 
Auxiliary 
Exhaust  Vatve- 


Exhaust 
Outlet 


Steam  Inlet 

FIG.  486. — Section  of  poppet-valve  engine  cylinder  of  Hamilton  uniflow  engine.  (Hooven 
Owens,  Rentschler  Co.) 

superheat  ordinarily  used  with  valves  of  various  types  is 
shown  in  the  following  table. 


SEC.  428]          SUPERHEATED  STEAM  IN  ENGINES 


421 


428.  Table  Showing  Maximum  Pressures  And  Superheats 
To  Which  Engine  Valves  Of  The  Various  Types  May  Be 
Subjected. 


Valve 

Pressure, 
Ib.  per  sq. 
in.  abs. 

Superheat, 
deg.  fahr. 

Total 
temperature, 
deg.  fahr. 

Flat  slide  valve          

125 

50 

395 

Corliss 

200 

120 

500 

Piston          

f!75 

200] 

Poppet 

j 
[250 

250 

i 
170  J 

200 

570 
600 

NOTE. — GOOD  PRACTICE  WITH  CORLISS  VALVES  Is  To  USE  MODERATE 
SUPERHEATS  (about  50  deg.  fahr.).  The  first  50  deg.  fahr.  superheat  is 
the  most  cheaply  obtained  and  is  more  beneficial  than  any  other  equal 
increase  in  superheat.  Higher  superheats  than  those  indicated  in  the 
table  are  occasionally  used  but  average  practice  is  much  lower  than  the 
values  given. 

429.  Metals   For  Valves   And   Seats  Which  Are   To  Be 
Used  With   Superheated   Steam  are   cast  iron,   cast  steel, 
Monel  metal  and  bronze.     For  safety  valves,  Monel  metal 
seats  and  valve  feathers  are  preferred  by  some  manufacturers. 
Soft  brasses  cannot  be  used.     Piston  valves  should,  prefer- 
ably, be  cast  from  the  same  heats  as  their  seats  to  insure 
equal  expansion  or  contraction  with  change  in  temperature. 
Superheated  steam  has  a  greater  tendency  to  cut  the  faces  of 
valves  when  the  valves  are  " cracked"  (nearly  closed)  than  has 
saturated  steam.     High-grade  cast  iron  is  used  for  Corliss 
and  poppet  valves  with  superheated  steam  up  to  about  550 
deg.  fahr.     It  has  some  tendency  to  "grow"  (suffer  a  perma- 
nent increase  in  size)  due  to  the  action  of  high-temperature 
steam.     Cast     steel  is  used  for  valve  bodies;     bronze  for 
piston-valve  bushings. 

430.  Cylinder  Oil  For  Engines  Using  Superheated  Steam 
must  be  a  high-grade  oil  which  will  not  decompose  at  the 
steam  temperature.     Highly  superheated  steam  will  not  con- 
dense in  the  cylinder  of  an  engine  when  operating  at  full  load. 
A  small  quantity  of  the  correct  heavy-bodied  cylinder  oil  will 
then  furnish  efficient  lubrication.     Friction  and  high  tern- 


422     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  14 

perature  have  a  tendency  to  decompose  unsuitable  oil  and 
form  carbonaceous  deposits.  Therefore  only  a  high-quality 
cylinder  oil  should  be  used.  An  engine  operating  under 
average  light-load  conditions  on  highly  superheated  steam 
requires  a  relatively  small  volume  of  steam  per  stroke,  which 
though  introduced  in  the  cylinder  in  a  dry  condition  will,  at 
the  end  of  the  stroke,  be  partially  condensed.  Also,  if  the 
steam  is  initially  only  moderately  superheated,  it  will  enter 
the  high-pressure  cylinder  in  dry  condition,  but  will  cool, 
and  toward  the  end  of  the  stroke  it  will  partially  condense. 
Under  these  conditions  a  medium-bodied  high-quality  cylinder 
oil  will  furish  efficient  lubrication.  A  number  2  or  number  3 
dark  straight  mineral  oil  is  recommended  in  Table  482  for 
most  superheated  steam  conditions.  The  Vacuum  Oil  Co. 
recommends  its  "  Gargoyle  cylinder  oil  600-W"  up  to  600  deg. 
fahr.  and  "  Extra  Hecla"  for  over  600  deg.  fahr.  total 
temperature. 

431.  Operating  Engines  On  Superheated  Steam  Does  Not 
Nepessarily   Involve   Any   Change    In    Operating   Methods. 
Engine  valves  and  lubrication  systems  must  be  such  as  to 
permit    the    contemplated    degree    of    superheat.     Metallic 
packing  (Fig.  369)  should  always  be  used  with  high-pressure 
superheated  steam  since  soft  packings  will  not  stand  the  high 
temperatures  and  pressures.     The  packing  gland  should  also 
be  independently  supplied  with  oil  of  a  high  grade  and  under 
pressure. 

NOTE. — OIL  Is  SUPPLIED  To  THE  CYLINDERS  AND  VALVES  OF  COUN- 
TERFLOW  ENGINES  EMPLOYING  SUPERHEATED  STEAM  preferably  by  the 
atomization  method,  as  explained  in  Sec.  502.  However,  oil  is  some- 
times admitted  through  openings  into  the  valve  chest.  The  piston  valve 
of  Fig.  485  is  supplied  with  oil  through  the  lining  around  its  central 
portion.  The  oil  is  led  through  a  pipe  to  the  small  annular  space  between 
the  two  halves  of  the  lining  from  which  it  is  carried  by  the  moving  valve 
and  later  taken  away  by  the  steam.  Uniflow  engines  are  supplied  with 
cylinder  oil  as  explained  in  Sec.  434. 

432.  The  Use  Of  Superheated  Steam  Partially  Obviates 
The   Desirability   Of   Compounding. — As    was   explained   in 
Sec.  273,  the  chief  purpose  in  compounding  is  to  decrease 
cylinder   condensation.     When   superheated   steam   is   used, 


SEC.  433]        SUPERHEATED  STEAM  IN  ENGINES 


423 


its  excess  heat  prevents  any  immediate  condensation  and 
may  keep  the  steam  dry  until  cut-off.  Moreover,  the  lesser 
heat  conductivity  of  superheated  steam  results  in  a  lesser 
transfer  of  heat  to  and  from  the  cylinder  walls.  Hence  it 
follows  that  the  economy  of  superheating  (Figs.  487  and  488) 
is  not  as  great  in  compound  and  triple-expansion  engines  as  in 

simple  engines.  Also  the  economy 
of  compounding  is  not  as  great 
when  superheated  steam  is  used 
as  when  the  steam  is  saturated. 
These  facts  are  evident  from  the 
following  table: 


34 
U32 
o:30 
*2S 
|26 
£24 
•21 

I20 

Elfl 

£  16 
3  14 

i« 

£10 

to 
8 

6 

\ 

\        \ 

\ 

••Simp/6. 
~30%A 

V        1 

'  Non-Conden 
Bating    I 

sing\ 

\ 

^ 

^ 

\ 

Sim} 

X 

&7S 

?%& 

on-L 
>af/; 

ondt 

rising 

V 

\ 

s 

^< 

Simple  Nt 

•>n- 
'ensi 
Cull 
"^^ 

Loa 

1— 

^ 

ona 

* 

"_> 

^ 

\ 

N 

/ 

^% 

•^ 

X 

^~^ 

"~~- 

>- 

\ 

^s 

^ 

'  

^~~» 

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Con 

Nor 
-Ful 
\ 

pet 

-Co 
1  Lo 

nd* 

^  — 

"~~-~ 

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isingr*" 

*•<, 

va 

V 

\       {     & 

Con 

ndei 

pou 
-/sine, 

ne( 

r  FUI 

'Hoc 

7d-; 

Indicated  Horse  Power 
,40  fcO  80  100  l?0  I40  160  180700  ?ZO  Z40J60J80300 


15   SO    75    100   115  150    175  700  225 
Degrees  Superheat 

FIG.  487. — Showing  the  effect  of 
superheat  on  a  simple  12  by  16-and  a 
compound  10  and  173-^  by  16  in.  pis- 
ton-valve Buckeye  engines.  (Steam 
pressure  100-110  Ib.  per  sq.  in.  Foster 
superheater  catalogue.) 


Per  Cent.  Load  On  Engine 


FIG.  488.  —  Graphs  showing  influence  of 
superheat  on  water-rate  (steam  consumption 
of  a  16  by  22-inch  "Ideal"  Corliss  engine. 


433.  Table    Showing    Savings    Effected    In    Engines    Of 
Different    Classes    By    Superheating    The    Supply    Steam. 

(Alexander  Bradley,  Power,  Sept.  2,  1919.) 


Engine 


Saving  in  per  cent,  due  to 

100  deg.  fahr.  superheat 

at  average  pressures 


Steam 
saving 

Heat 
saving 

Simple  engines  and  compressors 

18 

13  5 

Compound  engines  and  compressors  

14 

10.5 

Triple-expansion  engines  
Single  direct-acting  pumps 

12 
22 

9.0 
16  5 

Compound  direct-acting  pumps  

18 

13.5 

424    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  13 

NOTE. — Compound  and  multi-expansion  engines  benefit  more  by 
higher  steam  pressures  than  they  do  by  superheat.  Consequently  the 
practice  is  to  use  relatively  high  pressures  and  relatively  little  superheat 
with  engines  of  these  types. 

434.  In  Uniflow  Engines,  The  Use  Of  Superheated  Steam 
Is  Very  Economical  (Sec.  333).  Uniflow  engines  are  practi- 
cally always  simple  engines  but  are  installed  where  high 
economies  are  desired  and  are  commonly  operated  condensing. 
Under  these  conditions,  superheated  steam  is  a  decided  advan- 
tage and  is  nearly  always  used. 

NOTE. — IN  LUBRICATING  UNIFLOW-ENGINE  CYLINDERS,  it  is  better  to 
inject  some  of  the  oil  at  points  A  and  B  (Fig.  489),  than  to  mix  it  all  with 


Steam 
Supply-. 


5-feam 

. -Aa 'm/s s  i on     Va I  ve    Sea  t s  -      Supply-  • 
•-Oil  Leads- 


Relief 
Va/ve 


FIG.  489. — Showing  recommended  points  of  oil  injection  in  uniflow  engine.     (Arrows 
show  direction  of  steam  flow.) 


the  steam.  Due  to  the  nearly  straight  path  of  the  steam  in  a  uniflow- 
engine  cylinder,  the  oil  which  is  mixed  with  the  steam  has  much  less 
tendency  to  attach  itself  to  the  walls  of  the  cylinder  than  it  has  in  counter- 
flow  engines.  However,  when  injected  at  A  and  B,  the  oil  has  a  tendency 
to  flow  down  over  the  walls.  The  piston  then  spreads  it  over  the  cylin- 
der's length. 

435.  When  Superheated  Steam  Is  Used  In  Compound  Or 
Triple -Expansion  Engines,  the  steam  usually  becomes  satu- 
rated in  the  high-pressure  cylinder  before  release.  Hence, 
the  steam  enters  the  receiver  as  wet  steam.  A  reheater 
(Fig.  336)  is  frequently  used  under  these  conditions  to  super- 
heat the  steam  again  before  it  enters  the  next  lower-pressure 
cylinder;  see  the  " locomobile"  in  Fig.  395. 


SEC.  436]        SUPERHEATED  STEAM  IN  ENGINES 


425 


NOTE. — SIMPLE  ENGINES  ARE  PROFITABLY  OPERATED  AT  RELA- 
TIVELY Low  PRESSURES  AND  HIGH  SUPERHEATS.  For  mechanical 
reasons  high  pressures  are  not  desirable  in  simple  engines.  But,  for 
high  efficiency,  the  temperature  range  in  a  simple  engine  must  be  great. 
By  employing  high  superheats,  a  large  temperature  range  may  be 
secured  without  the  mechanical  difficulties  and  excessive  cylinder  con- 
densation (Fig.  490)  which  high  pressures  involve. 


5     10     15    20    25    30    35    40   45 
Percentage  Of  Stroke  Completed  At 
Cut -Off 

FIG.  490. — Graphs  showing  effect  of  superheated  steam  in  decreasing  cylinder  condensa- 
tion and  leakage  in  simple  engines.     (An  average  of  41  deg.  fahr.  superheat.) 


436.  A  Table  Showing  The  Advantages  And  Disadvantages 
Of  Superheated  Steam  as  compared  to  saturated  steam  for 
steam-engine  operation  is  as  follows: 


Advantages 


Disadvantages 


Increases  engine  efficiency. 
Decreases  the  amount  of  oil  needed. 
Requires  less  weight  of  steam  for  a 

given  amount  of  power. 
Decreases     cylinder     condensation 

and  trouble  with  water  in  engine 

cylinder. 

Decreases   radiation   and   pressure 


Requires  additional  equipment. 
Requires  a  better  grade  of  oil. 
Requires  high-temperature  packing. 

Where  impure  feed  water  is  used, 
dust  may  be  carried  from  the 
superheater  to  the  engine.  See 
note  below. 

May  cause  changes  in  shape  and 
size  of  cast-iron  parts. 


NOTE. — A  FOAMING  BOILER  MAY  GIVE  DANGEROUS  RESULTS  IF  THE 
STEAM  Is  SUPERHEATED.  The  foam  which  leaves  the  boiler  is  usually  a 
saturated  solution  of  some  mineral  which  was  used  as  a  scale  preventive. 
When  this  saturated  water  is  evaporated  in  a  superheater,  the  mineral 
remains  in  the  superheater  as  a  fine  dust.  After  a  quantity  of  dust 
accumulates  in  the  superheater,  some  of  it  will  be  carried  away  with 
the  steam  which  passes  to  the  engines.  As  this  mineral  dust  is  a  very 


426     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  14 

good  abrasive,  it  becomes  very  dangerous  in  that  it  will  probably  score 
the  engine  cylinder.  Foaming  of  the  boilers  is,  therefore,  to  be  particu- 
larly avoided  when  the  steam  leaving  the  boiler  is  later  superheated. 

QUESTIONS  ON  DIVISION  14 

1.  What  steam  saving  results  from  superheating  steam  for  simple  engines? 

2.  What  effect  has  superheat  on  cylinder  condensation? 

3.  Name  six  differences  between  superheated  and  saturated  steam. 

4.  What  is  an  approximate  relation  between  the  temperature  of  superheated  steam 
and  its  volume? 

5.  What  types  of  valves  are  preferred  for  highly  superheated  steam? 

6.  What  effect  in  the  valves  of  an  engine  is  noticed  due  to  the  lesser  fluid  friction  of 
superheated  steam? 

7.  What  is  the  approximate  limit  of  total  temperature  for  cast-iron  valves? 

8.  What  metals  are  used  in  valves  for  superheated  steam? 

9.  What  kinds  of  cylinder  oil  are  recommended  for  engines  using  superheated  steam? 

10.  How  is  oil  introduced  into  a  counterflow  engine  using  superheated  steam?     Into 
a  uniflow  engine? 

11.  What  kind  of  packing  should  be  used  for  highly  superheated  steam? 

12.  What  is  the  relation  between  compounding  and  superheating  in  steam-engine 
practice? 

13.  How  does  superheating  lessen  the  desirability  of  compounding? 

14.  When,  in  general,  are  high  pressures  and  slight  superheats  used?     When  low  pres- 
sures and  high  superheats? 

15.  What  is  the  usual  condition  of  the  exhaust  steam  from  the  high-pressure  cylinder 
of  a  compound  engine  using  superheated  steam? 

16.  Enumerate  the  principal  advantages  of  superheated  steam  for  engines. 

17.  Explain  why  a  foaming  boiler  is  dangerous  in  a  superheated-steam  plant. 


DIVISION  15 
SELECTING  AN  ENGINE 

437.  The  Governing  Factor  In  Selecting  An  Engine  Should 
Be  The  Cost  Per  Unit  Of  Energy  Delivered  by  the  engine. 
In  computing  the  cost  per  unit  of  energy  delivered  (Sec.  447), 
all  items  of  expense  must  be  considered.  An  engine  with  a 
very  low  initial  cost  may,  because  of  its  steam  rate,  produce 
power  at  a  much  higher  cost  than  a  more  expensive  engine 
which  uses  less  steam.  Conversely,  the  engine  which  uses 
least  steam — and  therefore  the  least  fuel —  will  not,  necessarily, 
produce  power  more  cheaply  than  a  less  expensive  engine 
which  uses  more  steam — although,  erroneously,  some  engineers 
consider  only  the  fuel  cost.  As  explained  in  following  sections, 
there  are  a  large  number  of  elements  which  enter  into  the 
computation  of  the  unit  energy  cost.  The  unit  energy  cost 
is  usually  computed  over  a  yearly  period,  thus : 

,     ,   n  Total  expenses  per  year 

(bo)  Cose  per  unit  of  energy  =  -^ -. — , — ; ; 

Energy  units  developed  per  year 

NOTE. — THE  TOTAL  ANNUAL  COST  OF  AN  ENGINE,  which  will  supply  a 
given  quantity  of  power  throughout  the  year  and  under  certain  condi- 
tions, is  frequently  used  as  the  governing  factor  in  selection;  but,  as 
explained  later,  the  total  annual  cost  then  bears  a  given  ratio  to  the 
unit  power  cost.  Thus,  it  is  immaterial  whether,  under  given  conditions, 
the  unit  energy  cost  or  the  total  annual  cost  is  taken  as  the  governing 
factor  in  engine  selection. 

NOTE. — THE  PROCEDURE  IN  SELECTING  AN  ENGINE  FOR  A  GIVEN 
SERVICE  consists  of:  (1)  A  study  of  requirements  and  operating  conditions 
Sec.  448,  to  determine  what  type  or  types  of  engines  are  best  suited  for 
the  service.  (2)  A  computation  of  the  unit  cost  of  energy  for  each  engine 
which  is  suited  for  the  service  and  which  it  is  desired  to  consider.  (3) 
A  choice  of  the  engine  which  affords  the  least  unit  energy  cost.  The 
sections  which  immediately  follow  deal  with  the  calculation  of  the  true 
unit  energy  cost.  After  this  are  given  considerations  of  service  require- 
ments and  more  specific  rules  for  engine  selection. 

427 


428    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  15 

438.  Various    Elements   Which   Are    Factors    In    Energy 
Cost  And  Which  Should  Be  Considered  In  Computing  The 
Cost  Per  Unit   Of  Energy   are   generally  grouped  into  two 
classes:  (1)  The  fixed  charges,  or  those  elements  of  cost  which 
are  the  same  whether  an  engine  is  operated  or  idle.     The  fixed 
charges,  as  explained  in  subsequent  sections,  comprise  interest 
on  invested  capital,  rentals,  insurance,  taxes,  and  depreciation, 
which  is  the  natural  loss  of  value  of  the  machine  as  its  age 
increases  (Sec.  443).     (2)  Operating  charges,  or  those  elements 
of  cost  which  are  proportional,  directly  or  otherwise,  to  the 
energy  developed  by  an  engine.     The  operating  charges,  as 
is  also  explained  in  subsequent  sections,  include  the  cost  of 
all  labor  involved  in  the  operation  of  the  engine,  the  costs  of 
all  materials  which  are   consumed  in  its  operation,  and  all 
costs   necessary  to  keep  it  in  a  good  operating  condition; 
such  as  the  cost  of  repairs,  replacements,  and  adjustments. 
These  operating  charges  are  frequently  termed  attendance, 
material,  and  maintenance  respectively. 

NOTE. — FIXED  CHARGES  ARE  OFTEN  COMPUTED  As  A  LUMP  SUM — 
that  is,  the  annual  amount  of  the  fixed  charges  is  taken  as  a  certain  per- 
centage of  the  total  first  cost.  A  common  percentage  for  this  purpose, 
which  experience  shows  to  be  fairly  accurate  for  average  conditions,  is 
15  per  cent.  Thus,  if  an  engine,  installed,  costs  $10,000,  the  fixed  charges 
may  be  taken  as  0.15  X  $10,000  =  $1500  per  year.  Why  15  per  cent, 
is  taken  rather  than  some  other  value  will  be  evident  from  a  study  of  the 
example  under  Sec.  446  wherein  the  total  of  the  fixed-charge  percentages 
is  15. 

439.  Interest  is  the  cost  of  the  capital — invested  money— 
in  any  undertaking.     Interest  is  a  rental  or  fee  paid  for  the 
use  of  money.     A  corporation  can  only  obtain  money  by 
borrowing  from   investors   who  always  demand  interest   (a 
rental)  in  payment  for  use  of  the  money.     If  the  borrowed 
money  is  used  to  purchase  an  engine,  the  interest  on  the  invested 
money  is  an  item  of  the  expense  incurred  in  operating  the 
engine.     Now,  even  if  one  uses  his  own  money — and  does 
not  have  to  borrow — in  purchasing  an  engine,  interest  should 
nevertheless  be  charged  in  when  determining  the  total  expenses 
per  year  of  the  engine.     One  must  consider  that,  if  the  engine 
had  not  been  purchased,  the  money  which  was  used  for  its 


SEC.  440]  SELECTING  AN  ENGINE  429 

purchase  could  have  been  invested,  kept  on  deposit,  or  loaned 
so  as  to  draw  interest.  If  the  money  is  invested  in  an  engine 
it  should  bring  at  least  the  same  return.  Therefore,  for  com- 
parative purposes  the  interest  on  the  money  invested  in  the 
engine  should  always  be  computed  and  recognized  as  an  item 
of  expense  incident  to  the  ownership  of  the  engine.  See 
example  under  Sec.  446  for  an  application  of  this  idea. 

NOTE. — THE  ANNUAL  INTEREST  EXPENSE  is  determined  by  the  amount 
of  the  initial  investment  and  by  the  current  interest  rate.  The  initital 
investment  includes  the  first  cost  of  the  engine,  its  accessories,  founda- 
tion, and  installation  together  with  all  transportation  charges.  The 
interest  rate  is  usually  6  to  8  per  cent,  per  year. 

EXAMPLE. — If  an  engine  installed  complete  costs  $10,000  and  the 
usual  interest  rate  in  the  community  where  it  is  installed  is  6  per  cent.; 
then  the  annual  interest  expense  of  operating  the  engine  =  10,000  X  0.06 
=  $600  per  year — and  this  $600  is  just  as  real  an  item  of  the  cost  of 
running  the  engine  as  is  the  cost  of  the  oil  and  waste  for  it  or  the  cost  of 
the  steam  which  operates  it. 

440.  Rent,  As  An  Item  Of  Engine  Expense,  Should  Be 
Charged  In  Proportion  To  The  Floor  Space  occupied  by  an 
engine  whether  the  building  in  which  the  engine  is  housed 
is  rented  or  not.     The   engine   and   its  accessories  occupy 
space  which  could  otherwise  be  used  for  some  other  purpose. 
The  fair  rent  which  this  space  could  command  is  justly  an 
expense  incident  to  the  keeping  of  the  engine.     Horizontal 
engines  occupy  space   about  as  follows:  Over  2000  h.p. — 
0.5  sq.  ft.  per  h.p.;  500  to  1000  h.p. — 1  to  2  sq.  ft.  per  h.p. 
Small  engines — 3  to  4  sq.  ft.  per  h.p. 

NOTE. — A  PORTION  OF  THE  ADMINISTRATION  OR  OFFICE  EXPENSE  OF 
A  PLANT  may  be  charged  to  an  engine,  according  to  its  value  as  compared 
with  that  of  the  rest  of  the  plant.  It  may,  however,  be  advisable  to 
group  the  engine  administration  expense  with  that  of  the  rest  of  the 
power-plant  equipment  and  then,  for  cost-estimating  purposes,  to  handle 
this  combined  item  as  a  single  item. 

441.  Insurance  Cost  Is  An  Item  Of  Engine  Expense  because 
it  is  a  direct  expenditure  for  protection  against  loss  by  fire 
or  other  hazards.     The  annual  cost  of  insurance  against  fire 
loss  is  small.     In  a  fireproof  building  it  is  ordinarily  less  than 
0.5  per  cent,  annually  of  the  amount  of  insurance  carried.     In 


430    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  15 

wooden  buildings  it  is  somewhat  greater.  An  average  value 
is  about  1.5  to  2  per  cent.  In  hazardous  locations,  such  as  in  a 
saw  mill-  where  the  fire  risk  is  great,  it  may  be  impossible  to 
get  any  insurance.  The  depreciation  rate  (Sec.  444)  should 
then  be  made  high  enough  to  cover  a  possible  loss  by  fire 
within  a  few  years. 

442.  Taxes  Constitute  An  Item  Of  Engine  Expense  because 
taxes  are  the  cost  of  government,  including  police  and  fire 
protection,  which  is  levied  on  all  property  in  proportion  to  its 
assessed  value.     Tax  rates  per  year  are  usually  1  to  2  per  cent, 
annually  of  the  assessed  value  of  the  property.     The  assessed 
value  is  generally  lower  by  a  considerable  amount  than  the 
first  cost.     The  actual  tax  rate  for  any  community  may  be 
ascertained  by  consulting  the  assessor.     After  the  tax  rate 
is  determined,  the  taxes  on  the  engine  should  be  included  in 
its  annual  expense.     Taxes  on  the  real  estate  on  and  in  which 
the  engine  is  housed  should  be  taken  account  of  in  computing 
the  rental  (Sec.  440)  and  should  not  be  included  as  a  direct 
engine  expense  under  the  heading  of  taxes. 

443.  Depreciation  is  the  decrease  in  value  of  a  thing  as  it 
becomes  older.     Any  piece  of  machinery  has  a  certain  useful 
life.     If  a  thing  has  a  life  of  10  years  and  no  scrap  value  and 
its  original  cost  is  $100,  it  is  evident  that  (disregarding  interest 
on  sinking  fund  and  other  refinements)  the  cost  per  year  of 
its  decrease  in  value  =  $100  -5-  10  =  $10.     From   this   it   is 
evident  that  depreciation  is  a  reasonably  definite  and  tangible 
item  in  the  cost  of  operating  an  engine.     Depreciation  may  be 
due  to:  (1)  Wear  and  tear;  continual  use  gradually  produces 
wear    at    all   of    an    engine's    bearing   surfaces.     Eventually 
it  may  be  impossible  to  properly  adjust  the  worn  parts.     The 
engine  will  then  be  useless.     (2)  Obsolescence;  improvements 
are  being  made  continually  in  the  principles  and  construc- 
tion of  steam  engines.     It  may  therefore  be  assumed  that, 
even  if  it  were  possible  to  maintain  an  engine  indefinitely  in 
good  running  order,  the  engine  would  eventually  have  to  be 
replaced  by  some  more  efficient  engine.     As  an  example  of 
obsolescence  may  be  taken  the  case  of  many  good  steam  engines 
which  were  in  use  when  the  steam  turbine  was  first  perfected. 
In  many  instances,  the  engines  were  so  much  less  efficient  than 


SEC.  444]  SELECTING  AN  ENGINE  431 

turbines  that,  though  new,  it  would  have  paid  to  replace  them 
with  turbines.  (3)  Inadequacy;  in  many  plants  the  demands 
for  power  increase  to  such  an  extent  that  it  becomes  econom- 
ically wise  to  discard  old  but  mechanically  good  engines  in 
favor  of  larger  engines.  Customarily,  it  is  not  attempted 
to  foretell  whether  an  engine  will  depreciate  because  of  wear 
and  tear,  obsolescence,  or  inadequacy;  but,  instead,  a  useful 
life  is  assumed  in  accordance  with  the  lives  which  experience^/'' 
shows  to  be  most  common;  see  following  section. 

NOTE. — THE  "DEPRECIATION  CHARGE"  OR  "COST"  OR  THE 
" ANNUAL  DEPRECIATION"  is  the  amount  which  should  be  considered 
as  an  annual  expense  incident  to  the  ownership  of  an  engine  (or  other 
equipment).  It  may  be  found  by  dividing  the  first  cost  of  the  engine  by 
its  useful  life  in  years.  It  should  be  understood  that  annual  depreciation 
charges  can  be  only  reasonably  accurate  estimates  or  guesses — it  is 
impossible  to  predetermine  depreciation  exactly.  The  depreciation 
charge  should  actually  be  paid  out — that  is,  it  should  be  placed  in  a 
bank  or  other  safe  depository.  The  sum  which  thus  accumulates  in 
the  depository  is  called  the  sinking  fund.  At  the  end  of  the  engine's 
useful  life  the  sinking  fund  should  equal  the  first  cost  of  the  engine  so  that 
the  engine  may  be  replaced  without  borrowing  new  capital  or,  if  the 
engine  is  no  longer  needed,  that  the  investors  may  be  paid  off.  To  be 
strictly  correct  it  might  seem  that,  since  the  sinking  fund  can  be  made  to 
draw  interest  and  since  at  the  end  of  its  useful  life  the  engine  still  has  some 
value  (see  below),  the  depreciation  charge  computed  as  directed  above 
will  provide  a  sinking  fund  which  will  exceed  the  engine's  true  deprecia- 
tion. But,  since  the  life  of  the  engine  is  not  definitely  known  before- 
hand, the  " straight-line"  method  of  computing  the  depreciation  charge, 
which  is  suggested  above,  is  sufficiently  accurate  for  practical  purposes. 

NOTE. — THE  RESIDUAL  VALUE  OR  SCRAP  VALUE  OF  AN  ENGINE  is  its 
value  at  the  end  of  its  useful  life.  Since,  at  the  end  of  its  useful  life,  an 
engine  has  no  value  as  an  engine,  its  residual  value  is  simply  the  value, 
as  scrap,  of  the  materials  of  which  it  is  made.  The  residual  value  of  an 
engine  seldom  exceeds  5  per  cent,  of  its  first  cost. 

444.  The  Usual  Depreciation  Rates  For  Steam  Engines 

are  determined  from  their  useful  lives.  Experience  shows 
that  the  average  lives  of  steam  engines  are  about  as  follows: 
High-speed  engines — 17  years.  Medium-speed  engines — 20 
years.  Low-speed  engines — 28  years. 

EXAMPLE. — If  the  first  cost  of  a  medium-speed  engine  is  $8000  what 
should  be  its  annual  depreciation  cost?  SOLUTION. — Since  the  probable 


432        STEAM  ENGINE  PRINCIPLES  AND  PRACTICE  [Div.  15 


100 


life  of  a  medium-speed  engine  is  20  years,  the  depreciation  rate  =  100 
-5-  20  =  5  per  cent.  Therefore,  the  annual  depreciation  cost  =  0.05 
X  $8000  =  $400. 

445.  The  Operating  Costs  Of  An  Engine  are :  (1 )  Maintenance, 
which  comprises  the  costs  of  repairs  and  such  replacements 
of  parts  as  are  occasionally  necessary.  The  maintenance 
cost  per  year  may  ordinarily,  for  estimating  purposes,  be 
taken  at  2  to  4  per  cent,  of  the  first  cost  of  the  engine.  (2) 
Materials.  These  are  steam,  engine  oil,  cylinder  oil,  packings, 
waste,  and  miscellaneous  supplies.  The  cost  of  steam  varies 

greatly  with  boiler  conditions  and 
the  price  and  kind  of  fuel.  With 
12,000  B.t.u.  coal  at  $5.00  per 
ton,  the  average  cost  of  producing 
steam  in  a  stoker-fired  water-tube 
boiler  plant  is  about  45  ct.  per 
1000  Ib.  For  the  same  coal  in  a 
hand-fired  return-tubular  plant,the 
cost  would  be  about  60  ct.  per  1000 
Ib.  In  any  plant,  the  cost  of  steam 
FIQ.  491. — showing  average  cyi-  per  pound  =  (total  annual  boiler- 

inder     oil     consumed     per     brake      7  \  /  7  /•  ? 

horsepower     hour    by     engines    of  P^nt  expense]    =    (number  of  pounds 

various  sizes.  of  steam  generated  per  year)',  see 

the  author's  STEAM  BOILERS.  The  cost  of  cylinder  oil  may 
be  based  on  the  average  cylinder-oil  consumptions  shown 
on  the  graph  of  Fig.  491.  The  amount  of  engine  oil  used 
varies  greatly  with  the  method  of  lubrication  and  the 
precautions  taken  for  its  recovery.  It  should  not  greatly 
exceed  the  amount  of  cylinder  oil.  The  cost  of  the  other 
materials  seldom  exceeds  10  ct.  per  h.p.  year  for  a  100-h.p. 
engine  to  2  ct.  per  h.p.  year  for  a  1000-h.p.  engine.  In  general, 
the  oil  and  other  supplies  constitute  about  2  to  9  per  cent,  of  the 
total  operating  expenses.  (3)  Attendance.  This  includes  the 
salaries  of  operating  engineers,  oilers,  and  a  portion  of  the 
salaries  of  superintendents  and  others  who  devote  part  of 
their  time  to  the  engine  or  in  supervising  its  attendants.  An 
operating  engineer  can,  ordinarily,  take  care  of  more  than  one 
engine;  but,  where  the  plant  is  operated  24  hours  per  day, 
three  engineers  are  probably  necessary. 


WO          100       1.000 
Brake  Horsepower  Of  Engine 


SEC.  446]  SELECTING  AN  ENGINE  433 

446.  The  Total  Annual  Cost  Of  An  Engine  is  the  sum  of  the 

annual  fixed  and  operating  costs.  The  meaning  of  this  is 
illustrated  in  the  following  example  which  gives  an  economic 
comparison  between  engines  of  two  different  types  which  are 
to  be  served  by  an  existing  boiler  plant. 

EXAMPLE. — Compare  the  annual  cost  of  a  poppet-valve  engine  with 
that  of  a  slide-valve  engine.  Both  are  rated  at  200  h.p.  and  both  are 
operated  non-condensing  on  saturated  steam.  The  poppet-valve  engine 
uses  18  Ib.  of  steam  per  i.h.p.  hr.  at  175  Ib.  per  sq.  in.;  the  slide-valve 
engine  uses  29  Ib.  of  steam  per  i.h.p.  hr.  at  125  Ib.  per  sq.  in.  Assume 
that  the  cost  of  the  steam  at  175  Ib.  per  sq.  in.  is  51  ct.  per  1000  Ib.,  and 
at  125  Ib.  per  sq.  in.  is  50  ct.  per  1000  Ib.  A  stand-by  unit  is  assumed  to 
be  necessary  in  each  case. 

SOLUTION.- — 

Fixed  charges: 

POPPET-     SLIDE-      POPPET-    SLIDE- 
VALVE      VALVE        VALVE      VALVK 

First  cost  of  one  engine $4,175   $2,225    $ 

Foundation  and  installation 625         625       

Total  first  cost. $4,800  $2,850       

Interest  at  6  per  cent. $  288     $      171 

Depreciation  based  on  an  18-year  life  at  5.55  per  cent. 

(100  -T-  18  =  5.55  per  cent,  per  year) 266  158 

Rent 70  60 

Taxes  and  insurance  at  2  per  cent 96  57 

Total  fixed  charges 720  446 


Doubling  this  value  to  include  stand-by  unit 1,440  892 

Operating  charges  (assuming  700,000  i.h.p.  hr.  of 
service  per  year,  that  is  200  h.p.  delivered  10  hours 
per  day  for  350  days) : 

Steam,  12,600,000  Ib.  at  51  ct.  per  1000  Ib 6,426 

20,300,000  Ib.  at  50  ct.  per  1000  Ib 10,150 

Oil  and  other  supplies 255  255 

Attendance 3,150  3,150 

Repairs  (guess  estimate) 115  95 

Total  operating  charges 9,946       13,650 


Total  annual  cost $11,386       14,542 

11,386 

Annual  saving  of  poppet-over  slide-valve  engine $  3,156 

28 


434     STEAM  ENGINE,  PRINCIPLES  AND  PRACTICE    [Div.  15 

The  obvious  conclusion  is  that,  for  the  conditions  specified,  the  poppet- 
valve  engine  is  the  more  economical.  This  is  because  of  its  lower  steam 
consumption.  If  the  steam  (coal)  were  cheaper  or  if  the  engine  were 
used  fewer  hours  during  the  year,  the  difference  in  the  annual  costs  would 
be  less  than  $3156  or  it  might  be  in  favor  of  the  slide-valve  engine.  It 
would  be  possible  to  decrease  the  initial  investment  for  the  poppet- 
valve  engines  by  using  a  cheap  engine  as  a  stand-by  unit.  The  standby 
unit  need  not,  ordinarily,  be  operated  more  than  a  week  in  each  year; 
hence  its  steam  consumption  would  be  of  relatively  minor  importance. 
There  are,  however,  many  advantages  in  having  both  the  working  and 
spare  engines  of  the  same  kind  (Sec.  452). 

447.  The  Unit  Cost  Of  The  Energy  which  is  generated  by 
an  engine  is  calculated  by  dividing  the  total  annual  cost  of 
an  engine  by  its  yearly  energy  output;  see  Sec.  437  and  also 
the  following  example. 

EXAMPLE. — If  the  engine  of  the  preceding  section  produces  annually 
650,000  h.p.  hr.  of  useful  mechanical  energy,  would  it  be  as  cheap  to  buy 
electrical  energy  (which  can  be  converted  into  mechanical  with  an 
efficiency  of  82  per  cent.)  for  4  ct.  per  kw.  hr.?  SOLUTION. — The  cost 
of  the  purchased  mechanical  energy  (converted  electrical  energy)  is 
4  -T-  0.82  =  4.9  ct.  per  kw.  hr.  From  the  engine,  the  mechanical  energy 
cost  =  (total  annual  cost)  -r-  (number  of  energy  units  produced)  =  $11,386 
-T-  650,000  =  $0.0175  or  1.75  ct.  per  h.p.  hr.  or  1.75  X  1000/746  =  2.35 
ct.  per  kw.  hr.  Therefore,  the  engine  develops  energy  at  a  lower  cost 
than  that  for  which  the  electrical  energy  can  be  bought. 

448.  Before  Endeavoring  To  Select  An  Engine  For  Any 
Given  Service,  the  following  factors  should  be  determined  or 
estimated:   (1)   Horse  power  of  engine.     (2)  Speed  of  engine. 
(3)  Operating  conditions,  such  as  the  initial  state — pressure  and 
temperature — of  the  engine's  steam  supply,  whether  the  engine 
is  to  be  operated  condensing  or  non-condensing,  the  boiler 
capacity,  and  the  cost  of  fuel.     If  the  engine  is  to  run  non- 
condensing  and  if  exhaust  steam  is  necessary  for  heating  or 
industrial  processes,  the  quantity  of  exhaust  steam  required 
should  also  be  known.     (4)  Operating  characteristics,  such  as 
the  load  curve  (see  Sec.  453),  the  expected  life  of  the  engine, 
and  the  types  of  the  other  engines  in  the  plant. 

NOTE. — IN  SELECTING  ENGINES  FOR  A  NEW  PLANT  the  operating 
conditions  are  not  usually  determined  definitely  until  after  the  type  of 
engine  which  will  be  used  has  been  selected.  Furthermore,  the  require- 
ments, as  to  horse  power  and  exhaust  steam  required,  can  frequently  be 


SEC.  449]  SELECTING  AN  ENGINE  435 

only  estimated.  However,  in  selecting  an  engine  for  addition  to  an 
existing  plant,  the  requirements  and  operating  conditions  are  usually 
better  known. 

449.  In  Determining  the  Proper  Horse  Power  Of  A  Contem- 
plated   Engine    two    things  should   be   considered:  (1)    The 
maximum  or  peak  load  which  the   engine  must  carry.     As 
engines   cannot  economically   develop   much   more   than   25 
per  cent,  overload  and  as  it  may  be  expected  that  the  power 
requirements  will  usually  increase  after  the  engine  is  in  service, 
the  engine  selected  should  have  a  normal  rated  capacity  at 
least  as  great  as  the  peak  load  which  it  must  carry.     (2)  The 
continuity  of  service  which  is  desired.     In  some  plants  the 
management  will  not  object  to  an  occasional  shut-down  of 
the  engines  for  repairs.     During  the  shut-down  power  may, 
in  some   cases,    be   purchased   from   another   company.     In 
other  plants,  electric-light  plants  in  particular,  there  must  be 
no  danger  of  having  ever  to  discontinue  any  of  the  power 
supply.     In  such  plants  the  units  should  be  so  selected  that, 
should  the  largest  unit  need  repair,  the  remaining  units  can 
carry  the  entire  load  which  may  come  on  the  plant. 

EXAMPLE. — If  a  power  plant  has  a  peak  load  of  400  h.p.,  and  if  shut- 
downs are  permissible,  the  plant  may  be  equipped  with  one  400-h.p. 
engine  or  two  200-h.p.  engines;  but,  if  shut-downs  must  be  avoided,  the 
plant  must  either  have  two  400-h.p.  engines  or  three  200-h.p.  engines, 
or  some  other  combination,  see  Sec.  453. 

450.  In  Determining  The  Desirable  Speed  Of  A  Contem- 
plated Engine  Or  Engines,  the  use  to  which  the  engine   is 
to  be  put  should  be  considered.     Generally  speaking,   elec- 
tric generators,  especially  alternating-current  generators,  are 
most  advantageously  driven  at  high  rotative  speeds  because 
high-speed   generators   cost   less   than    do  slow-speed    gene- 
rators.    High-speed  engines  may,  therefore,  be  direct-connected 
to  generators  whereas  slow-speed  engines  must  be  belted  to 
or   employ  larger   and   more   expensive   generators.     Where 
engines  are  not  used  to  drive  generators,  the  service  conditions 
almost  automatically  determine  the  most  desirable  speed.     In 
any  case,  the  desirability  of  a  certain  engine  speed  should  be 
considered  along  with  all  other  factors.     When  an  engine  is 
belted  to  its  load  the  ratio  of  the  speeds  of  the  driving  to  the 


436     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  15 

driven  pully  or  vice  versa  should  not  exceed  6  to  1;  4  or  5 
to  1  is  preferable. 

NOTE. — THE  SPEED  OF  AN  ENGINE  WHICH  DRIVES  A  DIRECT-CON- 
NECTED ALTERNATING-CURRENT  GENERATOR  is  definitely  determined 
by  the  desired  frequency  and  the  number  of  field  poles  of  the  generator, 
thus: 
(64)  r  9  .       -  120  X  frequency 

lOIJ  /.   p.  Trl.    —    •^r; ~7~f* — Tl 1 — 

No.  of  field  poles 

See  the  author's  AMERICAN  ELECTRICIANS'  HANDBOOK  for  further  informa- 
tion and  table  of  synchronous  speeds  for  the  various  frequencies  and 
numbers  of  field  poles. 

451.  In  Considering  The  Operating  Conditions  With 
Reference  To  The  Selection  Of  A  Contemplated  Engine  Or 
Engines  it  should  be  remembered  that:  (1)  The  state  of  the 
steam  supplied  to  the  engine  determines  to  a  degree  the  kind  of 
valves  which  the  engine  may  have;  see  Sec.  428.  (2)  Exhaust 
steam  requirements,  throughout  the  factory,  determine  whether 
a  low  steam  rate  is  necessary  or  even  desirable.  (3)  Condens- 
ing operation  is  advisable  under  certain  conditions  (see  Sec.  297), 
but,  in  other  cases,  is  not  necessary  or  even  desirable.  (4) 
Boiler  and  condenser  capacities  determine  whether  the  con- 
templated engines  will  necessitate  new  boilers  and  condensers 
and,  therefore,  additional  investment.  Sometimes  an  engine 
with  a  small  water  rate  can  be  installed  without  any  increase 
in  boiler  or  condenser  capacity,  whereas  a  cheaper  engine, 
which  would  otherwise  be  satisfactory,  would  require  the 
purchase  of  additional  equipment  because  of  its  higher  water 
rate.  (5)  Fuel  cost  determines  whether  a  low-water-rate  engine 
is  economically  preferable  for  a  given  service.  Where  fuel 
is  very  cheap,  as  in  saw  mills  and  coal  mines,  the  higher  first 
cost  of  an  economical  engine  may  not  be  justified  by  the  small 
fuel  saving. 

NOTE. — IN  SELECTING  THE  PROPER  BOILER  PRESSURE  FOR  A  NEW 
PLANT,  the  soundest  plan  is  to  find  the  unit  cost  of  energy  (Sec.  447) 
for  different  assumed  boiler  pressures  and  the  correspondingly  different 
engines  and  boilers.  That  pressure  is  then  chosen  which  provides  the 
least  unit  cost.  Generally  speaking,  high-pressure  boilers  are  more 
expensive  in  fixed  and  operating  costs  than  are  low-pressure  boilers. 
Nevertheless,  engines  operated  on  high-pressure  steam  are  always  more 
efficient  than  those  operated  on  low-pressure  steam  and,  usually,  the 


SEC.  452] 


SELECTING  AN  ENGINE 


437 


9UV 
£750 
o  600 

\\\\ 

Rate 

1  Output 

•\ 

J 

"• 

j 

5450 

I300 
o  ISO 
1  0 

{ 

1 

* 

J: 

•A  ve/agre/oaaf^4J2  Kw. 

Y 

J 

"^ 

* 

12    2 


10   12 


fixed  charges  are  less  for  the  engine  which  is  operated  on  high-pressure 
steam.  The  boiler  pressure  should  therefore  be  as  high  as  is  practical 
with  the  engine  which  is  best  suited  to  the  plant;  maximum  permissible 
pressures  and  superheats  for  the  engines  of  the  different  types  are  given 
in  Table  428. 

452.  The  Operating  Characteristics  Which  Affect  The 
Selection  Of  An  Engine  are:  (1)  The  load  curve  of  the  plant 
(Fig.  492).  The  load  curve  of  the  plant  is  the  graph  which 
shows  the  variation  from  time  to  time  of  the  required  total 
engine  output.  A  load  curve  might  be  plotted  for  any  par- 
ticular engine;  from  this  graph  can  be  read  the  portion  of  the 
total  time  that  the  engine 
must  carry  its  rated  full  load 
and  other  fractional  loads. 
These  portions  of  time  deter- 
mine to  a  large  extent  whether 
the  engine  should  have  good 
economy  or  not.  For  ex- 
ample, if  an  engine  is  to  be 
operated  a  great  portion  of 
the  time  at  only  one-fourth 
its  rated  capacity,  then  it 
should  be  selected  on  the  basis  of  its  steam  rate  at  one- 
fourth  load  rather  than  the  basis  of  its  full-load  steam  rate. 
Likewise,  if  an  engine  is  to  stand  idle  for  a  great  portion  of  the 
time,  since  its  fixed  charges  continue  while  it  is  not  in  opera- 
tion, the  operating  charges  may  constitute  but  a  small  fraction 
of  its  total  annual  cost;  hence  its  water  rate  is  of  relatively  little 
importance.  (2)  The  life  of  the  engine.  If  an  engine  is  to  be 
used  continuously,  its  life  will  of  course  be  shorter  than  if  it 
were  used  but  little.  However,  the  life  of  an  engine  is  fre- 
quently assumed  to  be  the  same  regardless  of  its  service 
because  it  gradually  becomes  useless  although  it  may  not  be 
wearing  out,  see  Sec.  443.  (3)  Other  engines  in  the  plant.  If 
a  plant  is  already  equipped  with  some  engines,  additional 
engines  which  are  to  be  installed  should,  unless  some  other 
consideration  is  more  important,  be  of  the  same  make  and  kind 
as  the  older  engines.  This  will  insure  a  better  understanding 
of  all  engines  and,  if  the  new  and  old  engines  are  exactly  alike, 


4     6     8    10    12     2    4     fc 
A.  M.  P.    M. 

Time 


FIG.  492. — Daily  load  curve  for  a  600-kw. 
electric  power  plant. 


438    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  15 


(65) 


Load  factor  = 


a  reduction  in  the  number  of  repair  parts  which  must  be 
stocked. 

NOTE. — THE  "LOAD  FACTOK"  OF  A  PLANT  may  be  taken  as  the  ratio 
of  its  daily  average  power  output  to  the  maximum  load  which  it  must 
carry.  The  daily  average  power  output  is  found  by  first  computing  the 
total  daily  energy  output  (kw.  hr.  or  h.p.  hr.)  and  then  dividing  this  value 
by  the  number  of  hours  in  the  day.  Stated  as  an  equation: 

Average  power  output 
Maximum  power  output 

EXAMPLE. — If,  in  Fig.  492,  the  average  power  output  is  found  to  be 
432  kw.,  what  is  the  load  factor?  SOLUTION. — Since,  in  Fig.  492,  the 
maximum  load  on  the  plant  is  750  kw.,  load  factor  =  432/750  =  0.58 
or  58  per  cent. 

453.  Engine  Sizes  Should  Be  Selected  To  Suit  The  Load 
Curve,  where  such  procedure  is  economically  feasible. 
Especially  in  large  plants,  where  a  number  of  engines  are 
required  to  carry  the  maximum  power  output,  the  engines 
may  be  so  selected  as  to  size  that  at  no  time  is  any  engine 
operating  at  a  small  fraction  of  its  rated  load.  This  can  best 
be  illustrated  by  an  example. 

EXAMPLE. — Let  graph  A,  Fig.  493,  represent  the  load  curve  of  a 
contemplated  plant.  It  is  desired  to  equip  the  plant  with  engines 

to  suit  the  load  curve.  It  is  evi- 
dent that,  from  midnight  to  5 
a.m.,  a  500-h.p.  engine  will  carry 
the  load.  It  is  also  evident  that, 
from  8  a.m.  to  5  p.m.,  the  load  can 
be  carried  by  engines  aggregating 
2500  h.p.,  whereas  the  maximum 
load  during  the  day,  which  occurs 
in  the  evening,  can  be  carried  by 
3000  h.p.  of  engines.  Suppose, 

FIG.  493.— Showing  method  of  operating  then,  that  the  plant  will  be 
engines  to  conform  to  the  load  curve  in  a  equipped  with  the  following  en- 


£T 

-}^ 

V 

s 

k 

g 

r—  • 

\i 

Q_ 

f 

A 

5 

T> 

/ 

t 

16 

d 

L 

jr 

ve 

\ 

.2 

7^ 

C 

I  '  ' 

^ 

—  inoo 

\ 

& 

I 

^ 

a 

r> 

fff 

Engint 

•> 

-o 

± 

K 

§      C 

\  \   1 

-1     i-z  •" 

f    4     6    6    10    12 
A.  M. 

4     fe    6    10   12 
R.M. 

large  plant. 


gines:  One  500-h.p.,  one  1000-h.p., 


and  two  1500-h.p.  (one  as  a  stand-by  or  emergency  engine).  Then 
the  load  can  be  carried  thus:  From  midnight  to  5  a.m.  only  the  500-h.p. 
engine  need  be  operated.  From  5  a.m.  to  8  a.m.  only  one  1500-h.p. 
engine  will  be  needed.  From  8  a.m.  to  5  p.m.  one  1500-h.p.  and  the 
1000-h.p.  engine  can  be  used.  Frem  5  p.m.  to  10  p.m.  the  two  1500- 
h.p.  or  one  1500-h.p.  together  with  the  two  smaller  engines  will  carry 
the  load.  From  10  to  11  p.m.  one  1500-  and  the  500-h.p.  engine  will 


SEC.  454] 


SELECTING  AN  ENGINE 


439 


suffice:  At  11  p.m.  the  500-h.p.  one  can  be  stopped,  the  load  until 
midnight  being  carried  by  the  large  engine.  Thus,  at  no  time  is  any 
engine  operated  under  a  small  fractional  load.  Still,  the  plant  can  be 
operated  at  all  times  with  any  unit  out  of  service. 

454.  The  Selection  Of  An  Engine  For  A  Given  Service 

involves  a  computation  of  the  unit  energy  costs  for  those 
various  engines  which  seem  to  suit  the  plant  requirements 
with  regard  to  horse  power,  speed,  operating  conditions  and 
plant  characteristics,  as  these  requirements  are  outlined  in 


0.60 

10.50 
a: 

1  0.40 

u 

w 
&-  0.30 
\n 

*>0.20 
o 

010 

\ 

\ 

^ 

Aft 

end 

?nc 

eCo 

5// 

>erl 

H./ 

>  Hr 

' 

\ 

N^ 

^ 

^ 

^ 

-  — 

-«-«. 

•?=-- 

•^—~. 

•*^-. 

—  -— 

"-  ~ 

—  - 

—  — 

•      • 

r=- 

—  _.  — 

i 

0  100        200        300       400         500        GOO        100        600        900        1000 

Indicated   Horse  Power 

FIG.  494. — Approximate  attendance  costs  for  steam  engines. 


the  preceding  sections.  After  the  unit  energy  costs  of  the 
various  engines  have  been  computed  (or  their  annual  costs, 
see  example  under  Sec.  446),  the  selection  can  be  readily  made. 
In  making  rough  estimates  as  to  engine  cost,  the  data  given 
in  Sec.  338  will  be  found  valuable.  The  water  rates  of  engines 
as  given  in  Div.  11  will  also  be  found  useful  in  estimating 
operating  costs.  Attendance  costs  may  be  taken  from  Fig. 
494  or  from  a  similar  graph. 

455.  A  Useful  Chart  For  Selecting  An  Engine  is  shown  in 
Fig.  495.  Each  black  space  in  the  chart  indicates  that  the 
type  of  engine  on  that  line  is  not  well  suited  to  the  condition 
of  its  vertical  column.  A  shaded  (cross-sectioned)  space 
indicates  that  the  engine  type  of  that  line  is  sometimes  used 


440    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE  [Div.  15 
for   the    condition   of  that  vertical   column.     White  spaces 


FIG.  495. — Engine-selection  chart.  To  use,  place  a  strip  of  paper  under  the  column 
heading  as  shown  in  Fig.  496  and  make  marks  in  the  proper  places  under  each  of  the 
eight  headings.  Then  slide  down  the  paper  until  a  line  is  found  where  no  black  spaces 
appear  before  the  marks.  A  line  in  which  no  shaded  or  black  spaces  appear  before 
the  marks  will  indicate  an  engine  which,  if  desirable,  may  be  used.  A  line  in  which 
black  spaces  appear  indicates  an  engine  which  is  not  well  suited.  See  also  Sec.  455. 


indicate  good  practice. 


Strip 
Of  Paper 


Chart 


It  is  to  be  remembered  that  such  a 
chart  can  only  be  an  aid  in 
selecting  an  engine  and  should 
not  be  relied  upon  to  give  the 
final  choice.  The  final  choice 
should  in  all  cases  be  made 
only  after  a  careful  study  of 
unit  energy  costs  for  the 
different  engines  (Sec.  454) 
which  may  be  employed  for 
the  condition  which  is  under 
consideration.  Fig.  496  shows 
how  to  use  the  chart. 

456.  Steam-Engine  Per- 
formance Guarantees  (Fig. 
497)  are  usually  included  with 
the  specifications  which  manu- 
facturers submit  with  their 
price  proposals  for  high-grade 
engines.  The  performance  guarantees,  when  written  or  printed 


FIG.  496. — Illustrating  method  of  using  the 
engine  selection  chart  of  Fig.  495. 


SEC.  456] 


SELECTING  AN  ENGINE 


441 


ALLIS-CHAIMERS  MANUFACTURING  COMPANY 

MILWAUKEE.  WISCONSIN.  U.S.A. 
SPECIFICATIONS    FOR 

ALLIS-CHALMERS  HORIZONTAL  SIMPLE  CORLISS  ENGINE 

r  ..........  Uni  ted.  State.  s..M.fg.?....Coin.pany.,...  .  ......  ---------------------  ..............  ------  .............. 


These  specifications  form  part  of  proposal  dated  ...........  J.8n.Uary...ls.i.*.....19.22........ 


Cylinder  diameter 


24. inches. 


.,150... 


Revolutions  per  minute 

Steam  pressure  at  throttle  valve 15.Q pounds  gauge. 

Superheat  at  throttle  valve.. ...Za.r.Q. degrees  Fah.  above  temperature  of  saturated  steam. 

Back  pressure  at  exhaust  nozzle.— - _      l4 pounds  gauge. 

Vacuum  at  exhaust  nozzle .Non-Condensing ....inches  of  mercury,      (BenrnE'»«er30") 

Engine  to  be  designed  to  operate  (Condensing  or  Non-condensing)  H.0n-Q.9n49.ns.ing ... 

Engine  to  be  (Right  or  Left).... -  .JAtt hand. 

Direction  of  rotation  of  wheel  (Over  or  Under) _ Under 

Direction  of  drive  (Away  from  or  Back  by  cylinders) Away. 

Crosshead  Pin ,  diameter 3i inches,  length 4.4 _ inches. 

Crank  Pin,  diameter. 4.4 inches,  length 3.4 inches. 

Main  Bearing,  diameter .7 inches,  length _ 14.... inches. 

Back  Bearing,  diameter...- .7 inches,  length... 13 .....inches. 

Wheel,  diameter _  ...ID. feet.    Approximate  weight .6.9.0.0. pounds. 

Wheel  face .2.1 —inches.    Type  of  wheel  (Belt,  Rope  or  Square  rim) .Belt. __ 

Wheel  to  be  crowned  for  belt  of  following  width IS". 

Wheel  to  be  grooved  for _ _ ..ropes inches  diameter. 


.49.00. 


Weight  of  heaviest  piece  of  engine,  approximately 

Width  and  Height  of  largest  piece  of  engine,  approximately  .........  ZZ 

Service  (What  will  the  engine  drive  and  how  will  it  be  connected  ?). 

...........................  Bfl.lla.d...to..  .Line  .....  Shaft  ......................  _  ..........................  __________  ......  _  ........  .  .....  ______________  .......  _  ............  _  ...........  .  ____ 

If  the  engine  is  to  drive  an  electric  generator  the  following  blanks  must  be  filled  in. 

GENERATOR  .................................  —  ...............  ...Kilowatts  at  .........................  %  Power  Factor  (....  ........  —  .............  K.  V.  A.) 

__________  .................  ...Current,  .....  ......  -  .....  _  ......  ..Cycles,  ............  ....  .  ......  Phase,..™  ....................  Volts,  ......  .  ...................  R.  P.  M. 

Generator  will  be  furnished  by  ----------------------  .....  —  .......  -  ...........  .............  —  .....  ------  .........  ...............  --------------------------------- 

Exciter  will  be  furnished  by_-  ................  --------------  ......  -  —  .....  --------  .........  —  •  -  .........  ----------  ...........  -  ......  -••••-  .......  -  ......  - 

How  is  exciter  to  be  driven—  .........  _  .......  ----  ......  -  ................  -  .......  .........................................  -•--  .................  ---------------  .......  -  .............. 


STEAM  CONSUMPTION— This  unit  when  operating  under  conditions  stated  on  Page  S  of  these 
specifications  will  require  not  to  exceed  the  following  pounds  of  steam  per  hour: 


LOAD 

Full  Load .2.5.0...... 

Three-quarter  Load -IB?. 

One-half  Load  1Z.S 


POUNDS  STEAM 

-I.  H.  P 21.8 Per1g=3P.— I.  H.  P 

-I.  H.  P 2.Q....8 Per  ySS-.—l.  H.  P. 

H.  P 22,1 Per  S53P.-I.  H.  P. 


A  tolerance  of  2%  from  figures  given  must  be  allowed  for  errors  in  obser- 
vation and  measurements. 


FIG.  497. — Manufacturer's  typical  performance  specifications  for  a  simple  non-condens- 
ing Corliss  engine. 


442    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  15 


ALLIS-CHALM ERS  MANUFACTURING  COMPANY 

MILWAUKEE.  WISCONSIN.  U.  S.  A. 


SPECIFICATIONS  FOR 

ALLIS-CHALMERS  HORIZONTAL  CROSS  COMPOUND 
CORLISS  ENGINE 

For Smith. .^d...jQne.8..Manuf»ctM.r.ing...Cpm.p.anjr.. 

These  specifications  form  part  of  proposal  dated 


...inches,  stroke Zf> 

...inches,  stroke 3.6 


High  pressure  cylinder,  diameter 1.6. 

Low  pressure  cylinder,  diameter ?.? _.. 

Revolutions  per  minute 1.20 

Steam  pressure  at  throttle  valve 150. pounds  gauge 

Superheat  at  throttle  valve .l.P.Q degrees  Fah.  above  temperature  of  saturated  steam. 

Back  pressure  at  low  pressure  exhaust  nozzle Q.Ond.eaB.itlg pounds  gauge. 

Vacuum  at  low  pressure  exhaust  nozzle .26 inches  of  mercury.        (**8Si£tM") 

Engine  to  be  designed  to  operate  (Condensing  or  Non-condensing)  Cond ensing 

High  pressure  side  to  b«  (Right  or  Left) .light. hand. 

Direction  of  rotation  of  wheel  (Over  or  Under) :...0.v«r. 

Direction  of  drive  (Away  from  or  Back  by  cylinders) v 

Crosshead  Pins,  diameter 4.B. inches,  length 6. inches. 

Crank  Pins,  diameter 6 inches,  length 5. inches. 

Main  Bearings,  diameter .14. inches,  length 2.0 inches. 

Wheel,  diameter 14 feet.    Approximate  weight .2.2000 pounds. 

Wheel  face inches.    Type  of  wheel  (Belt,  Rope  or  Square  rim) S3uar.e...rim 

Wheel  to  be  crowned  for  belt  of  following  width 

Wheel  to  be  grooved  for ropes _ inches  diameter. 

Weight  of  heaviest  piece  of  engine,  approximately 1.PP.P.P ... .    pounds 

(E«eluilv«  ot  .h«rl) 

Width  and  Height  ol  largest  piece  of  engine,  approximately 48 inches  x 48 inches. 

<E«!uil«.  at  »M) 

Service  (What  will  the  engine  drive  and  how  will  it  be  connected?) 

P.J.r.e.«*...OPxine.c.t.«4...to...50.Q..X.VA..aLt.er.iaating..curr*nt.  generator. 

If  the  engine  is  to  drive  an  electric  generator  the  following  blanks  must  be  filled  in. 

GENERATOR 40.P Kilowatts  at $>....%  Power  Factor  ( 5.P.Q K.  V.  A.) 

...Alternating Current 6p Cycles, 3 Phase 4.8?...,. Volts .1.20 R.  P.  M. 

Is  parallel  operation  required X8..? 

Generator  will  be  furnished  by This. .company 

Exciter  will  be  furnished  by This  company 

How  is  exciter  to  be  driven Belted,  to ...pulley,  on ...engine  .shaft 

STEAM  CONSUMPTION— This  unit  when  operating  under  conditions  stated  on  Page  5  of  these 
specifications  will  require  not  to  exceed  the  following  pounds  of  steam  per  hour: 

LOAD  POUNDS  STEAM 

Full  Load  .....4PP. <  640 ) K   w _( L  H   p)     20 . $ (12 . 8 ; )    per  K  w _(  j  H   p) 

Three-quarter  Load 3PP (.493.) K.  W.-(I.  H.  P.)....2.!..'.P J.MrlJLper  K.  W.-(I.  H.  P.) 

One-half  Load          .....29P 1.350 1 K.  W.-( I.  H.  P.>....?3.:.$ (13.-3 )...Per  K.  W.-( I.  H.  P.) 

NOTE — A  tolerance  of  2%  from  figures  given  must  be  allowed  for  errors  in  obser- 
vation and  measurements. 


§•* 

o  £ 


**" 


4)    >i 

§    § 


SEC.  456] 


SELECTING  AN  ENGINE 


443 


14 


£  16  'Saturated Steam,  Condensing: 


100  ° Superheat-  Condensing 

"Til' 


25         50         15         100 
Per  Gent.  Of  Rated  Load 


175 


Fia.  498. — Manufacturer's  guar- 
antees for  a  uniflow  engine  which 
is  to  operate  on  steam  at  150  Ib. 
per  sq.  in.  gage,  exhausting,  when 
non-condensing,  against  no  back 


in  specification  form,  constitute  what  is  called  a  performance 
specification.  In  a  performance  guarantee,  a  manufacturer 
will  usually  agree  that,  under  certain  operating  conditions, 
his  engine  will  have  certain  water  rates  at  full  load  and  at 
certain  fractional  loads.  The  graphs  of  Fig.  498  represent 
a  manufacturer's  guarantees.  The 
purchaser  may,  in  the  contract, 
demand  that,  if  the  guarantees 
are  not  fulfilled  in  an  acceptance 
test,  either  he  will  not  accept  the 
engine  or  that  the  price  shall  be 
proportionately  decreased  to  pen- 
alize the  manufacturer  for  failing 
to  meet  his  guarantee.  If  a  penalty 
is  stipulated,  the  manufacturer  will 
often  demand  (and  is  entitled  to) 
a  proportionate  bonus  or  increase  Pressure  and  when  condensing  into 

.  .  a  26-in.  vacuum. 

in    price    if    the    acceptance    test 

should    show    better    results    than    were    specified    in    the 

guarantee. 

NOTE. — THE  ACCEPTANCE  TEST  may  be  conducted  in  the  manufac- 
turer's factory  in  the  presence  of  the  purchaser's  representative,  or  after 
the  engine  is  erected  in  the  purchaser's  plant.  If  there  should  be  any 
doubt  of  obtaining  the  specified  operating  conditions  during  the  accept- 
ance test,  the  contract  may  be  made  to  include  the  basis  of  correcting 
the  test  results  to  the  specified  conditions.  To  insure  that  the  correc- 
tions will  be  properly  made,  manufacturers  frequently  are  required  to 
state  their  guarantees  for  a  wide  variety  of  operating  conditions  of  which 
one  is  certain  to  approximate  the  expected  conditions  of  the  test. 

NOTE. — To  CORRECT  TEST  RESULTS  To  STANDARD  OR  SPECIFIED 
CONDITIONS — see  following  illustrative  example — the  following  approxi- 
mate rules  may  be  used:  (1)  For  each  pound  difference  in  initial  pres- 
sure, correct  the  steam  consumption  by  from  0.1  to  0.2  per  cent.  (2) 
For  each  10  deg.  of  superheat,  up  to  100  deg.  of  superheat,  correct  the 
steam  consumption  by  1  per  cent.  (3)  For  each  inch  of  vacuum, 
between  24  and  28  in.  of  mercury,  correct  the  steam  consumption  by 
0.5  per  cent. 

EXAMPLE. — An  engine  acceptance  test  shows  a  steam  consumption 
at  Y±  load  of  22  Ib.  per  i.h.p.  hr.  The  actual  operating  conditions  were: 
Steam  pressure  160  Ib.  per  sq.  in.;  superheat  50  deg.  fahr.;  vacuum 
27  in.  of  mercury.  What  would  be  the  approximate  steam  consumption 
at  the  same  load  (^  load)  with  steam  at  175  Ib.  per  sq.  in.,  superheated 


444    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  15 

75  deg.  fahr.,  and  with  a  vacuum  of  25  in.  of  mercury?  SOLUTION.  — 
Applying  a  correction  of  0.15  per  cent,  for  each  pound  of  pressure: 
Correction  for  pressure  =  0.15  X  (175  -  160)  =  2.25  per  cent.  Super- 
heat correction  =  1  X  (75  —  50)  /10  =  2.5  per  cent.  Vacuum  correction 
=  0.5  X  (27  —  25)  =  1  per  cent.  Now,  since  steam  consumption 
decreases  with  increased  pressure,  higher  superheat,  and  increased 
vacuum,  the  net  correction  —  1  —  2.5  —  2.25  =  —3.75  per  cent.  Or,  the 
required  steam  consumption  =  22  -(0.0375  X  22)  =  21.2  Ib.  peri.h.p.  hr. 

457.  Things  Which  Should  Be  Specified  When  Requesting 
A  Quotation  On  A  Steam  Engine  are  as  follows:  (1)  Size  —  give 
bore  and  stroke  desired  or  horse  power  required.  (2)  Type  — 
vertical  or  horizontal;  simple,  tandem-  or  cross-compound; 
uniflow  or  counterflow;  center  crank  or  side  crank;  if  side 

crankj  whether  right  hand  or 
left  hand.  (3)  Speed—  normal 
speed  or  limits  between  which 
speed  must  be  varied.  (4) 
Steam  pressure  (and  superheat 
if  any)  upon  which  the  engine 


FIG.  499.—  Illustrating  meaning  of  "belt    is      to      be      Operated.       (5) 

forward"  and  "belt  backward."  emOT—  throttling  Or  CUt-off.      (6) 

Valve  type  —  whether  slide,  piston,  Corliss  or  poppet.  (7) 
Back  pressure  or  condenser  vacuum  which  will  be  maintained. 
(8)  Water  rates  desired  at  full  load  and  at  fractional  loads.  (9) 
Speed  regulation  —  allowable  variation  in  speed  from  full  load 
to  no  load  due  to  sudden  or  gradual  changes  in  load.  (10) 
Drive  —  whether  by  belt,  rope,  or  direct-connection.  (11) 
To  run  over  or  under.  (12)  Belt  or  rope  forward  or  backward 
(Fig.  499)  —  if  for  belt  or  rope  drive.  (13)  Foundation  plan  — 
if  space  is  restricted  specify  space  limits.  (14)  Base  — 
whether  desired  or  not.  (15)  Accessories  desired  with  engine 
—  electric  generator,  condenser,  lubrication  system,  foundation 
anchor  bolts,  etc.  (16)  Freight  —  state  whether  manufacturer 
shall  pay  freight. 

NOTE.  —  IF  AN  ELECTRIC  GENERATOR  Is  To  BE  FURNISHED  WITH 
THE  ENGINE,  the  generator  should  be  fully  specified.  The  voltage,  load 
characteristics,  number  of  phases  and  wires,  frequency,  method  of  excita- 
tion, whether  exciter  and  exciter  belt  and  pulleys  are  to  be  furnished, 
and  other  electrical  accessories  which  are  required  should  be  specified. 

NOTE.  —  IF  A  PUMPING  ENGINE  Is  To  BE  FURNISHED,  the  capacity, 
discharge  pressure,  suction  head,  and  pipe  sizes  should  also  be  specified- 


SEC.  457] 


SELECTING  AN  ENGINE 


445 


QUESTIONS  ON  DIVISION  15 

1.  What  factor  should  form  the  basis  upon  which  engines  are  selected?     Define  cost 
per  unit  of  energy. 

2.  Define  fixed  charges.     Tell  what  costs  are  considered  as  fixed  charges? 

3.  Define  operating  charges.     What  costs  constitute  operating  charges? 

4.  By  what  approximate  rule  may  fixed  charges  be  computed?     What  percentage  of 
the  first  cost  are  the  fixed  charges  in  the  example  of  Sec.  446? 

5.  Why  must  interest  be  considered  as  a  fixed  charge?     What  rate  is  usually  used? 

6.  Why  must  rent  be  always  considered  as  a  fixed  charge?     If  a  company  owns  its 
own  power  plant  building,  how  is  the  rental  charge  justified? 

7.  How  may  insurance  and  tax  rates  be  determined? 

8.  Explain  fully  why  depreciation  must  be  considered  as  a  fixed  charge.     What  is  a 
sinking  fund? 

9.  What  are  the  customary  depreciation  rates  for  steam  engines?     Explain  the  use  of 
a  sinking  fund  table.     What  is  the  straight  line  method  of  computing  depreciation? 

10.  List  all  the  operating  costs  of  a  steam  engine.     Which  of  these  is  usually  the 
largest? 

11.  Define  total  annual  cost.     How  is  it  related  to  the  cost  per  unit  of  energy? 

12.  Explain  fully  how  the  horse  power  of  a  contemplated  engine  is  decided  upon. 

13.  What  consideration  must  be  given  to  engine  speed  when  making  a  selection? 
Why? 

14.  What  influence  do  operating  conditions  have  on  the  selection  of  an  engine? 
Explain  fully  and  give  the  reasons. 

15.  What  operating  characteristics  must  be  considered  in  selecting  an  engine?     How 
do  they  affect  the  unit  cost  of  energy? 

16.  Explain  the  use  of  the  chart  of  Fig.  495  for  selecting  an  engine.     Does  the  chart 
afford  an  accurate  means  for  making  a  wise  selection?     Why? 

17.  What  are  performance  guarantees?     What  is  a  performance  specification?     How  are 
they  useful? 

18.  How  may  performance  guarantees  be  corrected  to  different  operating  conditions 
than  those  of  the  test? 

19.  Write  a  sample  letter  requesting  a  quotation  on  an  engine,  giving  all  information  it 
may  be  desirable  for  the  manufacturer  to  know. 


PROBLEMS  ON  DIVISION  15 

1.  An  engine  has  a  constant  load  of  250  h.p.  for  10  hours  per  day  and  300  days 
of  the  year.     If  its  total  cost  for  the  year  is  $15,000,  what  is  the  cost  per  unit  of  energy? 


1,500  - 

I  1  1  1  1 

V 

1   1    ' 

~—  ' 

-i 

5 

Rated  Full  L 

oc 

M 

-J 

1 

in 

*      : 

Actu 

a 

'lo 

art 

E 

i 

•TS  500 

•> 

9n 

24     68»    IT    2466    10   12 
A.  M.                          P.  M. 

Time 
FIG.  500. — Load  curve  of  plant  in  Prob.  3. 

2.  If  the  engine  of  Prob.  1  cost  $5000,  and  may  be  expected  to  be  useful  for  28  years, 
what  will  be  its  depreciation  charge? 

3.  A  1000-h.p.  non-releasing  Corliss-valve  engine  will  cost  $10.00  per  h.p.  including 
erection,  whereas  a  uniflow  engine  of  the  same  capacity  will  cost  $13.00  per  h.p.     The 
Corliss  engine  will  have  the  following  steam  rates:  at  %  load — 29.0  Ib.  per  i.h.p.  hr. ; 


446    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.   15 

at  K  load— 23.9  lb.;  at  H  load— 23.0  lb.;  at  full  load— 23.9  lb.  per  i.h.p.  hr.;  at  1M  load— 
24.9  lb.  The  uniflow  steam  rates  are:  at  K  load — 20.3  lb.  per  i.h.p.  hr.;  at  >£  load — 
19.6  lb.;  at  $i  load— 19.6  lb.;  at  full  load— 20.1  lb.;  at  ll/i  load— 21.0  lb.  The  cost  of 
steam  is  50  ct.  per  1000  lb.  Other  operating  costs  amount  to  $1.50  per  hour  of  service. 
The  plant  is  to  operate  300  days  per  year.  Fixed  charges  may  be  taken  at  15  per  cent, 
of  the  total  first  cost  of  the  engine.  If  the  load  curve  of  the  plant  is  as  shown  in  Fig.  500, 
find  the  unit  energy  costs  for  each  of  the  engines. 

4.  If  in  Prob.  3  either  another  uniflow  engine  or  a  Corliss  engine  would  be  necessary 
as  a  stand-by  unit  which  would  probably  be  operated  15  days  out  of  the  year,  which 
would  it  be  wise  to  install?  What  would  be  the  unit  energy  cost  of  the  protection 
against  shut-down? 


DIVISION  16 
STEAM-ENGINE  LUBRICATION 

458.  The  Purpose  Of  All  Lubrication  Is  To  Reduce  Friction. 

Friction,  it  is  known,  causes,  enormous  financial  losses  in 
plants  where  machinery  is  employed.  These  losses,  of  course 
cannot  be  entirely  prevented;  but,  in  many  cases  they  can 
be  very  greatly  reduced  by  the  careful  selection  and  use  of 
lubricants.  Before  attempting  to  discuss  problems  of  lubrica- 
tion it  may  be  well  to  study  the  causes  and  effects  of  friction 
in  machine  or  engine  bearings. 

459.  Friction  Is  A  Force  Which  Resists  The  Motion  of 
one  body  or  particle  over  another  body  or  particle   with 
which  it  is  in  contact.     There  are,  briefly,  three  forms  of 
friction:  (1)    Rolling   Friction    Between  Solids  (Fig.  501),  as 
in   a   ball   or   roller   bearing.     (2)    Sliding  Friction   Between 
Solids  (Fig.  502) ,  as  in  a  plain  bearing  or  between  a  piston  and 
cylinder.     (3)    Fluid   Friction    Between    The    Particles  Of  A 
Fluid  (Fig.  503),  as  with  water  or  steam  flowing  in  currents. 

460.  Rolling  Friction  Between  Solids  Direction  of  R0mng 
may  be  explained  by  a  consideration  of 

the  microscopic  structure  of  the  solids, 
Fig.  501.  The  surfaces  of  all  solids 
are  known  to  be  covered  with  very 
small  projections  and  depressions  as 
shown.  When  one  body  rests  upon 
the  other,  these  projections  interlock 
partly  and  prevent  motion.  Should  an  .  FIG  soi.-Magnified  sec- 

tion    through    small    ball    or 

attempt  be  made,  however,  to  roll  the  roller  in  roiling  contact  with 
one  on  the  other  as  shown  in  Fig.  .501,  another  solid- 
the  upper  body  will  have  to  be  raised  slightly  as  it  is  rolled 
over  a  projection  and  will  then  fall  again.  Its  movement, 
as  it  rolls  along,  will  consist  of  a  series  of  rises  and  falls.  The 
center  of  the  body  will  travel  a  zig-zag  line  as  shown.  Then, 

447 


448     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Drv.  16 

too,  the  rolling  body  will  be  slightly  ''flattened  out"  where  it 
touches  the  other  body  (as  occurs  with  a  partially  inflated 
automobile  tire).  This  flattening  out  is  accompanied  by  a 
movement  between  the  particles  which  compose  the  body. 
This  movement  is  again  resisted  by  internal  forces  between  the 
particles.  Hence,  this  resistance  comprises  the  rolling  friction 
between  the  bodies. 

NOTE. — "WEAR"  Is  THE  RESULT  OF  THE  BREAKING-OFP  OP  THE 
PROJECTIONS,  Fig.  501.  If  only  the  projections  were  broken  off,  one 
might  imagine  that  eventually  the  outline  of  the  body  would  be  a  smooth 
curve;  but,  wherever  a  projection  breaks  off,  a  depression  is  formed  in 
its  place  leaving  the  material  adjacent  to  the  original  projection  so  that 
it  forms  a  new  projection. 

461.  Sliding  Friction  Between  Solids  (Fig.  502)  is  similar 
to  rolling  friction.     The  chief  difference  between  the  two  is  in 
the  number  of  small   projections   (on  the  contact  surfaces) 
which  are  interlocked.     In  sliding  friction,  the  areas  of  the 
contact  surfaces  are  large,  whereas  in  rolling  friction  they 
are   usually   microscopic.     With   sliding  friction   (Fig.   502), 
as  with  rolling  friction,  the  two  bodies  must  be  separated 

slightly  from  one  another  as  they  move 
one  upon  the  other.  But  in  sliding  fric- 
tion this  separation  is  effected  against  the 
action  of  the  forces  which  tend  to  hold  the 

?A  Motion  Of      f    %         .       ..  ,.  __  .  . 

Piece  A    Fofce||     bodies    together.     Now,    since    the    force 
which  tends  to  slide  the  bodies  one  on  the 

FIG.  502.— Magnified          ,.  ,.  .  ,. 

section  of  two  solids  in    other    must    separate    them    against    the 

sliding  contact  without    action  of  forces,  it  is  obvious  that  it  must 

do  work  to  effect  sliding. 

NOTE. — THE  FORCE  REQUIRED  To  SLIDE  ONE  OF  THE  BODIES  ON 
THE  OTHER  is  the  force  required  to  overcome  friction.  The  resistance 
which  one  of  the  bodies  opposes  to  sliding  on  the  other  is  sliding  friction. 

462.  Fluid    Friction  Between  The   Particles   Of  A  Fluid 

may  be  explained  by  a  study  of  the  velocity  of  a  fluid  when 
flowing  through  a  pipe  (Fig.  503).  Actual  measurements 
show  that  this  velocity  is  not  the  same  at  all  points  in  the  pipe's 
cross-section  but  that  it  is  a  maximum  at  the  center  and  a 


Motion  of 


Fo 


Pie 


•;c. 


SEC.  463] 


STEAM-ENGINE  LUBRICATION 


449 


"Direction  of  flow 
FIG.  503. — Velocity  of  a 
fluid  in  a  pipe  is  not  the 
same  at   all   points  in  [its 
cross-section. 


minimum  at  the  wall.  In  fact,  no  accurate  measurement 
can  be  made  exactly  at  the  wall  of  the  pipe  and  it  is  very 
probable  that  there  the  velocity  would  be  zero.  The  velocity 
at  any  point  on  a  diameter  ab,  Fig.  503,  is  represented  graph- 
ically by  the  distance  from  ab  to  the  curve  xy.  Now,  since 
the  velocity  is  not  the  same  at  any  two 
adjacent  points  on  any  diameter  as  ab,  it 
is  evident  that  adjacent  particles  of  the 
flowing  liquid  will  be  moving  upon  one 
another.  This  movement,  however,  is 
resisted  by  internal  forces  between  the 
particles  of  the  fluid.  The  total  resist- 
ance comprises  the  fluid  "friction"  in 
the  pipe.  In  other  words,  fluid  friction 
is  the  resistance  offered  by  one  particle  of  a  fluid  to  the  sliding 
over  it  of  another  particle  of  the  fluid.  In  general,  fluid  fric- 
tion is  very  much  less  than  sliding  or  rolling  friction. 

463.  Fluid  Friction  Replaces  Sliding  Friction  when  a  fluid 
is  introduced  (Fig.  504)  between  the  sliding  surfaces  of  two 
solids  and  kept  there.     The  fluid  adheres  to  each  solid  in  suffi- 
cient quantity  to  separate  the  solids  and  thereby  prevent  the 
projections  of  one  from  interlocking  with  those  of  the  other. 
The  fluid  then  divides — some  of  it  moves  with  one  solid  and 

some  with  the  other.  The  fluid  can  be 
thought  of  in  layers  which  slide  upon  one 
another  with  fluid  friction.  The  amount 
of  fluid  friction  will  depend  on  the  fluid 
used.  The  advantage  of  thus  substituting 
fluid  friction  for  sliding  friction  between 
the  solids  is  that  the  net  amount  of  friction 
is  thereby  greatly  reduced  and  "wear"  is 
practically  eliminated. 

464.  The  Reason  Oils  Are  Used  Between  Bearing  Surfaces 
is  that  they  possess  the  two  properties  most  necessary  for  a 
bearing   fluid:  (1)    A  bearing  fluid  must  "wet"  the  surfaces; 
that  is,  it  must  adhere  to  the  surfaces  strongly  enough  that  it 
will  of  itself  divide  into  layers,  some  of  which  will  travel  with 
each  of  the  sliding  solids.     (2)  It  must  "stand  up";  that  is, 
its  particles  must  cling  together  strongly  enough  that  the  fluid 

29 


force 


rorcc 


Fio.  504.— Magnified 
section  of  two  solids  in 
sliding  contact  with 
lubrication. 


450    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 

will  not  be  squeezed  out  under  the  action  of  the  forces  between 
the  solids  (Fig.  504)  which  tend  to  press  the  solids  together. 
These  properties  are  respectively  termed:  (1)  Adhesion 
and  (2)  cohesion  and,  together,  are  called  "body."  They  are 
present  in  different  oils  to  varying  extents.  The  significance 
of  "body"  in  the  selection  of  lubricants  for  specific  purposes 
is  discussed  in  Sec.  465. 

EXAMPLE. — WATER  HAS  GREAT  ADHERING  PROPERTIES  but  lacks  the 
clinging.  Mercury  again  exceeds  in  cohesion  but  lacks  adhesion. 
Hence,  neither  of  these  liquids,  would  make  a  good  lubricant. 

465.  The   "Viscosity"   Of  A  Liquid   is    a   measure   of  its 
internal   fluid   friction   or   its   resistance   to   flow.     A   high- 
viscosity  oil  is  "thick"  and  flows  slowly.     A  low-viscosity 
oil  is  "thin"  and  flows  readily.     The  viscosity  of  an  oil  is 
usually  measured  by  finding  the  time  required  for  a  certain 
amount  of  the  oil  to  flow  through  a  small  tube.     Besides  being 
a  measure  of  its  fluid  friction,  the  viscosity  of  an  oil  is,  to  a 
certain  extent,  a  measure  of  its  body.     See  Sec.  472  for  a 
method  of  measuring  viscosity. 

NOTE. — THE  VISCOSITY  OF  AN  OIL  CHANGES  WITH  ITS  TEMPERATURE, 
decreasing,  for  any  oil,  as  the  temperature  of  the  oil  is  raised.  It  is 
essential,  therefore,  that  one  know  the  viscosity  of  an  oil  at  the  tem- 
perature at  which  it  is  to  be  used. 

466.  Lubricants    May    Be    Grouped   Into  Three  Classes, 

namely:  (1)  Solids.  (2)  Semi-solids.  (3)  Oils.  Each  class  will 
be  discussed  separately,  with  its  uses,  in  the  following  sections. 

467.  Solid  Lubricants  Are  Occasionally  Used  to  smooth 
out  bearing  surfaces  by  filling  the  small  depressions  (Fig.  501). 
Graphite,  talc,  soapstone,  and  mica  are  solids  which  have 
lubricating  uses.     A  small  percentage  of  the  solid  lubricant 
is  usually  mixed  with  a  semi-solid  lubricant  and  the  mixture 
is  then  fed  to  the  bearings.     Sometimes  solid  lubricants  are 
introduced  separately  to  bearings  which  are  also  lubricated 
with  oil.     Solid  lubricants  cannot  be  squeezed  from  bearings 
and  will,  therefore,  often  keep  a  bearing  cool  where  no  other 
lubricant  will.     Experiments  have  shown  that  immediately 


SEC.  468]  STEAM-ENGINE  LUBRICATION  451 

after  a  temporary  application  to  an  oiled  bearing,  of  solid 
lubricant  in  powder  form,  the  friction  in  the  bearing  is  greatly 
increased,  but  is  reduced  after  the  particles  have  had  time  to 
attach  themselves  to  the  rubbing  surfaces  and  form  a  smooth 
coating.  The  virtue  of  a  solid  lubricant  lies  in  the  effect 
which  it  has  of  filling  the  depressions  in  the  bearing  surfaces 
themselves. 

468.  Semi-Solid  Lubricants  are  those  which  will  not  flow 
at  ordinary  room  temperatures.     They  are  commonly  known 
as  " greases."     They  are  desirable  for  lubricating  bearings 
in  places  where  the  air  is  filled  with  dust  and  grit,  as  in  rolling, 
cement,  and  other  similar  mills.     Greases  are  also  desirable 
in  applications  where  bearings  are  subjected  to  rather  high 
temperatures.     Greases  have  the  property  of  filling  bearing 
cavities  and  thereby  effectively  keeping  out  foreign  matter. 
They  may  also  be  used  in  bearings  into  which  it  would  be 
difficult  to  introduce  oils,  as  in  shaft-governor  and  similar 
bearings. 

NOTE. — GREASES  ARE  To  BE  USED  ONLY  WHERE  THERE  Is  SOME 
GOOD  REASON  FOR  NOT  USING  OIL  because  the  lubricating  properties  of 
greases  are  poor.  Unless  a  grease  melts  in  a  bearing  it  produces  consider- 
able friction.  If  it  does  melt  it  does  not  lubricate  as  well  as  an  oil. 

469.  Oils   Are    Of    Three    General   Kinds:    (1)    Mineral 
oils  are  distilled  from  the  crude  petroleums  found  in  many 
parts  of  the  world.     In  the  distillation  processes  a  great  num- 
ber of  grades  of  oil  are  obtained.     (2)  Fixed  (animal  and  vege- 
table)  oils  are   obtained  by  rendering  the  fatty  tissues  of 
animals  or  by  pressing  the  seeds  or  fruit  of  plants.     Fixed  oils 
cannot  be  distilled  without  decomposition.     They  are  affected 
more  or  less  by  the  oxygen  in  the  air  which  causes  them  to 
form  solid  deposits  or  varnishes.     They  also  decompose,  forming 
acids  which  will  attack  bearing  surfaces.     They  are  generally 
not  so  easily  squeezed  from  a  bearing  as  are  mineral   oils, 
because  they  possess  more  adhesion.     (3)   Compounded   oils 
are  mixtures  of  mineral  oils  with  small  percentages  of  fixed 
oils.     Compounding    a  mineral  oil  improves  its  adhesion  and 
makes  it  less  likely  to  be  washed  from  the  bearing  by  water 
(as  in  an  engine  cylinder);  but  it  renders  the  oil  more  liable 


452    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 

to  gum  and  cause  corrosion  and,  if  the  oil  is  to  be  used  again, 
makes  it  harder  to  separate  from  entrained  water. 

NOTE.  —  METHODS  OF  HANDLING  OIL  BARRELS  are  shown  in  Figs. 
505  and  506. 


.To  Oil  Receptacle 


liPipe--- 


''Connection  For 
Air  Hose 
(I Lb.  Pressure) 

'Brass 
Air  Pipe 


Oil  Barrel- 


Fia.  505.  —  Method  of  emptying  a  barrel  of  oil  with  compressed  air.  (It  is  claimed 
that  with  this  arrangement  a  barrel  of  cylinder  oil  can  be  emptied  in  5  min.  and  a  barrel 
of  engine  or  other  light  oil  in  3  min.  The  air  pressure  should  be  throttled  down  and  used 
with  considerable  caution.  Any  restriction  of  the  oil  discharge  or  an  attempt  to  force 
the  oil  out  against  a  considerable  head  will  result  in  bursting  the  barrel.  The  method  can 
not  usually  be  applied  effectively  for  very  heavy  oils.  It  is  useful  only  for  oils  forced 
against  low  heads.  (Southern  Engineer.) 


FIG.  506. — Arrangement  whereby  a  barrel  of  oil  can  be  rolled  up  an  inclined  plane  by  one 

man. 


470.  Oils  Can  Be  Tested  For  Certain  Properties  which 
may  determine  whether  or  not  an  oil  is  suited  for  a  particular 
use.  The  most  important  tests  are  for  the  following  properties 


SEC.  471] 


STEAM-ENGINE  LUBRICATION 


453 


of  an  oil:  (1)  Specific  Gravity.  (2)  Viscosity.  (3)  'Flash 
and  Fire  Points.  (4)  Chill  Point.  These  tests  will  be  discussed 
in  following  sections.  Besides  these  a  useful  test  is  one  to 
determine  the  extent  to  which  impurities  are  present  in  the 
oil.  Impurities  can  easily  be  re- 
moved by  straining  the  oil 
through  muslin  or  silk  cloth. 

471.  Its  Specific  Gravity  Indi- 
cates The  Source  Of  An  Oil  And 
The   Method   Used   In  Its   Re- 
finement.— The   specific   gravity 
of  an  oil  is  the  ratio  of  its  density 
(at  60  deg.  fahr.)  to  the  density 
of  water  (at  60  deg.  fahr.).     It 
can  conveniently  be  found  (Fig. 
507)  by  floating  a  "  specific  grav- 
ity" hydrometer,  H,  in  a  jar  of 
the  oil  and  reading  the  scale,  S, 
of  the  hydrometer  at  the  level 
of  the  oil.     The  specific  gravity 
of   an  oil  has  no  direct  bearing 
on     its    lubricating    properties. 
Oils    made    from    asphaltic-base 
crudes    will    generally    have    a 
higher  specific  gravity  than  oils 
of    a    paraffin-base    crude.     Oils 
treated  by  acid  will  have  higher 
specific  gravities  than  oils  treated 
by  filtration. 

472.  For   Measuring  Viscosity 
Of  An    Oil   (Sec.   465),   a    Say- 
bolt   viscosimeter    (Fig.    508)   is 
usually    employed.     The     reser- 
voir, B,  is  filled  with  the  oil  to 

be  tested  until  the  oil  begins  to  overflow  into  C,  and  the 
temperature  of  the  bath,  A,  is  brought  to  that  at  which  the 
measurement  is  to  be  made.  The  stopper,  D,  is  then  with- 
drawn and  oil  flows  from  B  through  the  outlet  tube,  F, 
into  the  glass,  G.  With  a  stop-watch,  time  is  taken  until  the 


<—Hyd 

srg 

r^.-£f: 

r_^^r: 

^-/ 

=:H  h 

1 

Observer's 
Eye 


-Graduated  Scale 


--Glass 
Hydrometer 
Jar 


-   ---Hollow  Par f 


End 


^\V\^ 

FIG.  507. — Illustrating  a  hydrom- 
eter and  its  use  in  finding  the 
specific  gravity  of  an  oil. 


454    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 


glass  is  filled  to  the  mark.  Care  must  be  exercised  that  no 
sediment  or  other  obstruction  collects  in  the  tube,.  F.  The 
temperatures  at  which  oils  are  tested  for  viscosity  are  usually: 
(1)  Cylinder  oils  at  212  deg.  fahr.  (2)  Oils  for  external  use 
at  104  and  140  deg.  fahr. 


Thermometer- 


Overflow 

Cup  -,    r      .-Reservoir  for 
"          '  Oil to  be  Tested 


<2 


FIG.  508. — Section  through  a  Saybolt 
viscosimeter. 


Fia.  509. — Section  through  Cleve- 
land open-cup  tester  for  flash-  and  fire- 
point  tests. 


473.  The  Flash  Point  Of  An  Oil  determines  whether  it  is 
relatively  good  or  bad  for  use  where  at  high  temperatures  it 
contacts  with  air.  The  flash  point  is  the  temperature  at  which 
the  oil  will  take  fire  from  a  flame  presented  at  its  surface. 

The  "fire  point"  is  the  temperature  at  which  this  fire  at  the 
surface  will  continue  after  the  flame  is  removed.  The  flash 
point  is  determined  by  heating  the  oil  (Fig.  509)  in  a  vessel 
which  is  either  in  direct  contact  with  a  small  flame  or  in  a 
bath  of  oil,  and  applying  a  flame  periodically  to  its  surface 
until  the  oil  takes  fire  at  the  surface.  An  oil  which  will  flash 


SEC.  474] 


STEAM-ENGINE  LUBRICATION 


455 


Cold  Test 
Thermometer 


at  a  low  temperature  is  evidently  not  suited  for  air-compressor 
cylinder  lubrication. 

474.  The  Chill  Point  Of  An  Oil  determines  whether  or  not  it  is 
fitted  for  a  system  where  it  will  be  exposed  to  low  tempera- 
tures.    The  chill  point  is  the  freezing  (or  melting)  tempera- 
ture of  the  oil.     It  may  be  conveniently  found  (Fig.  510) 
by  freezing  the  oil  in  a  test  tube  with  a  suitable  thermometer. 
(Cold-test  thermometers  are  scaled  for 

immersion  to  a  certain  mark  on  the 
stem.)  After  the  oil  is  frozen  the  test 
tube  with  the  frozen  oil  in  it  is  with- 
drawn from  the  freezing  mixture  and  is 
held  in  an  inclined  position  until  the  oil 
begins  to  flow  within.  The  temperature 
at  which  the  oil  begins  to  flow  is  the 
chill  point. 

NOTE. — THE  MELTING  POINT  OF  A  GREASE 
may  be  found  as  above  by  heating  the  grease 
in  a  test  tube  until  it  begins  to  flow. 

475.  In    Selecting    An   Oil  For  Any 
Purpose,   there  are  three   requirements 

which  must  be  satisfied:  (1)  The  oil  must  suit  the  mechanical 
conditions  of  the  bearing.  (2)  It  must  suit  the  lubricating  sys- 
tem. (3)  It  must  not  form  deposits  as  it  comes  in  contact  with 
various  substances  while  performing  its  functions. 

476.  The   Mechanical   Conditions   Of  A  Bearing  are:  (1) 
The  smoothness  of  its  surfaces.     (2)   The  rubbing  speed.     (3) 
The  pressure  on  the  journal  or  bearing.     (4)  The  temperature 
of  the  bearing.     They  affect  the  selection  of  on  oil  as  follows: 
(1)  Rough  surfaces  require  oils  of  greater  viscosity  and  body  than 
do  smooth  surfaces  because  rough  surfaces  must  be  kept  farther 
separated  by  the  oil.     (2)  Bearings  with  high  rubbing  speeds 
do  not  require  oils  with  as  much  body  as  do  those  with  low 
rubbing  speeds  because  the  higher  speeds  work  the  oil  into  the 
bearings  faster  and  do  not  give  the  " squeezing"  influence  of 
the  bearings  as  much  time  to  get  rid  of  the  oil  as  do  low  rubbing 
speeds.     (3)  Bearings  subjected  to  high  pressures  must  have 
oils  of  comparatively  high  viscosity  and  body  to  keep  the  oil 
from  being  squeezed  out,  whereas  in  bearings  which  operate 


FIG.  510. — Simple  appa- 
ratus for  finding  chill  point 
of  an  oil. 


456     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 

under  light  pressures,  a  light-bodied  oil  may  be  used  and 
benefit  derived  by  its  lesser  fluid  friction.  (4)  Oils  for  bearings 
that  are  situated  in  regions  of  high  temperature  or  for  bearings 
to  which  heat  may  readily  flow  must,  since  oils  lose  their 
viscosity  and  body  as  their  temperatures  are  raised,  be  supplied 
with  relatively  high-viscosity  oils. 

477.  How   The   Lubricating   System   Affects   The   Choice 
Of  An  Oil  can  best  be  understood  by  one  or  two  examples. 
Where,  for  instance,  bearings  are  fed  by  hand,  an  oil  must  be 
used  which  will  hold  a  film  until  the  bearing  is  again  oiled. 
But  where  a  continuous  stream  of  oil  is  fed  to  the  bearings, 
the  oil  need  not  be  of  the  same  quality.     Likewise,  in  a  system 
where  an  oil  is  to  be  cleaned  and  used  over  again,  the  oil  must 
be  one  which  will  separate  readily  from  impurities  which  it  may 
collect. 

478.  Certain  Oils  May  Form  Deposits  when  they  come  into 
contact    with   the    air,    gases,    or    other   substances.     These 
deposit-forming    oils  would,  of  course,  be  unsuited  for  use 
in  places  where  such  deposits  would  be  likely  to  occur,  even 
though  they  may  satisfy  the  mechanical  conditions  of  the 
bearings  and  the  lubrication  system.     In  the  steam  engine 
deposits  are  apt  to  be  formed  by  (1)  water,  (2)  solid  impurities, 
(3)  the  air  or  by  (4)  adding  new  oil  to  an  old  supply.     Whether 
or  not  an  oil  will  form  deposits  can  best  be  ascertained  only 
after  a  thorough  trial  of  the  oil  in  the  system  where  it  is  to  be 
used. 

479.  The  Selection  Of  Oils  For  Steam-Engine  Lubrication 
can  be  greatly  facilitated  by  the  use  of  the  following  tables 
and  Fig.  511  which  are  from  THE  PRACTICE  OF  LUBRICATION 
by  T.  C.  Thomsen.     The  descriptive  terms  applied  to  the 
oils  have  reference  to  methods  used  in  their  distillation  and 
refinement  and  cannot  be  explained  here;  see  PRACTICE  OF 
LUBRICATION.     The  oiling  systems  referred  to  will  be  described 
in  subsequent  sections. 

480.  Table  Of  Properties  Of  Circulation  Oils.— All  circula- 
tion oils  must  separate  rapidly  from  water.     Circulation  oil 
No.  1  is  a  neutral  filtered  oil.     Circulation  oil  Nos.  2  and  3 
are  mixtures  of  a  neutral  filtered  oil  with  filtered  cylinder 
stock. 


SEC.  481] 


STEAM-ENGINE  LUBRICATION 


457 


Saybolt  viscosity  in 

Circulation 
oil  No. 

Specific 
gravity 

Flash  point 
(open  cup), 
deg.  fahr. 

seconds 

Chill  point, 
deg.  fahr. 

At  104  deg. 

At  140  deg. 

fahr. 

fahr. 

1 

0.870 

395 

135 

70 

20-25 

2 

0.900 

410 

265 

120 

35-40 

3 

0.900 

425 

500 

200 

35-40 

481.  Table  Of  Properties  Of  Cylinder  Oils. 


Saybolt 

Specific  gravity 

Open  flash 
point,  deg.  fahr. 

Cold  test,  deg. 
fahr. 

Cylinder  oil 

viscosity 

at  212°F., 

seconds 

Filtered 

Dark 

Filtered 

Dark 

Filtered 

Dark 

No.  1  filtered  

85-105 

0.885 

500 

40-50 

No.  2  filtered,  No.  2  dark 

115-135 

0.887 

0.900 

525 

520 

50-60 

40-50 

No.  3  filtered,  No.  3  dark 

145-165 

0.890 

0.905 

550 

530 

50-60 

40-50 

No.  4  dark 

180-200 

0.910 

... 

580 

50-60 

NOTE. — CYLINDER  OILS  MAY  BE  COMPOUNDED  WITH  ACIDLESS 
TALLOW  OIL,  or  may  be  used  without  compounding.  The  following 
tables  show  their  uses  in  each  state. 


482.  Table    Of    Cylinder  Oil  Grades.— The  uses  of  each 
grade  are  given  in  Fig.  511. 


Grade  of  oil 


Designation 


No.  1  filtered  cylinder  oil,  heavily  compounded  (10  per  cent.) 
No.  1  filtered  cylinder  oil,  lightly  compounded  (4  per  cent.) 
No.  2  filtered  cylinder  oil,  medium  compounded  (6  per  cent.) 
No.  3  filtered  cylinder  oil,  medium  compounded  (6  per  cent.) 
No.  2  dark  cylinder  oil,  medium  compounded  (6  per  cent.) .  . 
No.  3  dark  cylinder  oil,  medium  compounded  (6  per  cent.) .  . 
No.  3  dark  cylinder  oil,  heavily  compounded  (10  per  cent.) .  . 
No.  4  dark  cylinder  oil,  medium  compounded  (6  per  cent.) .  . 

No.  2  filtered  cylinder  oil,  straight  mineral 

No.  2  dark  cylinder  oil,  straight  mineral 

No.  3  filtered  cylinder  oil,  straight  mineral 

No.  3  dark  cylinder  oil,  straight  mineral 


1  F.H.C. 

1  F.L.C. 

2  F.M.C. 

3  F.M.C. 

2  D.M.C. 

3  D.M.C. 

3  D.H.C. 

4  D.M.C. 
2  F.S.M. 

2  D.S.M. 

3  F.S.M. 
3  D.S.M. 


458     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 


FIG.  511. — Lubrication  chart  for  steam  cylinders  and  valves.  (From  PRACTICE  OF 
LUBRICATION  by  T.  C.  Thomson.) 

NOTE  1. — For  light-load  conditions  choose  an  oil  slightly  lower  in  viscosity  or  more- 
heavily  compounded  than  the  one  indicated  by  the  chart. 

NOTE  2. — With  impure  steam  (priming  boilers)  a  filtered  oil  should  preferably  be  used, 
and  with  saturated  steam  preferably  a  compounded  oil. 

NOTE  3. — When  the  chart  recommends  more  than  one  grade,  the  one  lowest  in  vis- 
cosity should  preferably  be  chosen.  When  a  dark  oil  as  well  as  a  filtered  oil  is  indicated, 
as  will  often  be  the  case,  the  former,  unless  there  are  special  conditions  (NOTE  2)  may  be 
preferred  as  it  is  (or  ought  to  be)  lower  in  price. 

NOTE  4. — A  straight  mineral  oil  can  always  be  used  in  place  of  the  compounded  oil 
recommended  by  the  chart  but  it  means  an  increased  oil  consumption  as  compared  with 
a  medium  compounded  oil  of  50  to  100  per  cent.  The  use  of  a  straight  mineral  oil  in 
place  of  a  lightly-compounded  oil  or  the  latter  in  place  of  a  heavily-compounded  oil 
means  an  increase  in  oil  consumption  of  30  to  50  per  cent. 

NOTE  5. — From  10  to  15  per  cent,  of  compounding  may  be  required  in  case  of:  (a) 
Very  wet  steam  in  large  engines,  low-pressure  cylinders  in  particular,  (b)  Heavily-loaded 
Corliss  valves  or  unbalanced  slide  valves,  (c)  Very-dirty  steam,  particularly  saturated 
steam. 

NOTE  6. — No.  2  FSM  and  3  FSM  will  separate  easier  from  the  exhaust  steam  than  No.  2 
DSM  and  3  DSM  and  will  give  a  cleaner  and  better  lubrication,  particularly  under 
conditions  of  superheated  steam  or  impure  steam. 


SEC.  483] 


STEAM-ENGINE  LUBRICATION 


459 


NOTE. — To  USE  THE  CHART  OF  FIG.  511  cut  a  strip  of  paper  long 
enough  to  extend  across  the  chart.  Then  for  each  of  the  seven  factors 
which  are  specified  along  the  top  of  the  chart,  make  a  mark  on  the  paper 
in  line  with  the  condition  of  the  engine  to  lubricate.  There  should  be 
seven  marks  on  the  paper.  Then  slide  down  the  paper  until  a  line  is 
reached  when  no  shaded  spaces  appear  in  the  same  columns  as  the  marks 
on  the  paper.  Then  read  off  at  the  left  the  oil  to  be  used. 

483.  Table  Of  Uses  Of  Bearing  Oils  In  Steam  Engines 

oiled  by  the  gravity-circulation  or  drop-feed  system.      (See 
Sees.  488  and  493.) 


Bearing  oil 

Saybolt  vis- 
cosity at  104°F., 
seconds 

Circulation  sys- 
tems, engine 
h.p. 

Drop-feed     sys- 
tems, engine  h.p. 

No  2 

120 

Below  250 

Below  100 

No.  3  
No  4 

175 
250 

250  to  400 
Above  400 

100  to  250 
250  to  500 

Nos.  5,  6  

450-700 

1  Special  cases 

Above  500 

only 

1  By  "Special  Cases"  is  meant  where  the  bearing  pressures  are 
extremely  high,  where  they  have  large  clearances,  or  where  they  are  so 
situated  that  their  temperatures  are  likely  to  be  high  by  reason  of  heat 
flow  from  some  nearby  hot  object. 

NOTE. — In  circulation  systems  or  where  the  oil  is  used  over  and 
over,  a  straight  mineral  oil  must  be  used.  Otherwise  a  compounded 
oil  may  be  used  if  desirable. 

484.  Table   Of  Oils  For  Use  In  Force-Feed  Circulation 

Systems.— (See   Sec.   494   and   Table   480.) 


Engine  size 


Circulation  oil  number 


For  engines  below  150  h.p. . 
For  engines  150  to  400  h.p. 
For  engines  over  400  h.p. . . 


No.  1 
No.  2 

No.  3 


NOTE. — Some  engines  have  unusually  heavy  connections  between  the 
cylinder  and  the  crank  case  permitting  a  large  amount  of  heat  to  flow 
down  to  the  crank  case.  For  such  engines  and  where  the  bearings  have 
unusually  large  clearances,  engines  below  250  h.p.  require  circulation 
oil  No.  2  and  those  above  250  h.p.  require  No.  3. 


460    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 


485.  Table  Of  Oils  For  High-Speed,  Splash-Oiled  Engines. 

(See  Table  480  and  Sec.  492.) 


Engine  description 

Grade  of  oil 

Percentage 
of  oil  in 
bath 

Small       horizontal       engines 
(stationary)  
Small    horizontal    engines    in 
vehicles  

Circulation  No.  1  or  No.  2 
Circulation  oil  No.  3  or  an 
oil  of  even  higher  viscosity 

100 
100 

Vertical  engines  below  50  h.p.. 

Vertical  engines  50  to  300  h.p.  . 
Vertical  engines  above  300  h.p. 

Circulation   oil    No.    2  or 
cylinder  oil  No.  2  F.L.C. 
Cylinder  oil  No.  2  F.L.C. 
Cylinder  oil  No.  3  F.M.C. 
or  cylinder  oil  No.  3  D.  M.  C 

15 
4  to  6 
4  to  6 
3  to  4 
3  to  4 

486.  Lubrication    Systems   For    Steam   Engines   may   be 

divided  into  two  clasess:  (1)  Systems  for  lubricating  external 
bearings.  External  bearings  are  those  which  are  not  enclosed 
within  the  parts  of  the  engine  which  hold  steam.  (2)  Systems 
for  lubricating  internal  bearings.  The  internal  bearings  of  a 
steam  engine  are  the  piston,  cylinder,  valves,  and  stuffing 
boxes.  Every  engine  will  employ  one  system  of  each  of  the 
above  classes.  The  principal  systems  of  each  class  will  be 
described  and  discussed  in  the  following  sections. 

NOTE. — SYSTEMS  FOR  EXTERNAL-BEARING  LUBRICATION  MAY  BE 
FURTHER  CLASSIFIED  into:  (1)  Automatic  systems,  in  which  the  oil  is 
repeatedly  used  in  the  bearings  and  needs  replenishment  only  to  make 
up  for  losses  by  evaporation  and  leakage.  (2)  Non-automatic  systems, 
in  which  the  oil  is  used  by  a  bearing  but  once  and  is  then  no  longer 
available  for  lubrication  unless  it  is  collected  by  an  attendant  and 
replaced  into  the  system. 

487.  Lubrication  Of  External  Bearings  By  Hand  is  the  most 
primitive,  wasteful,  and  unreliable  of  systems.     This  system 
should,  preferably,  never  be  used  on  all  parts  of  steam  engines. 
Hand  lubrication  is  that  method  in  which  the  oil  is  applied 
directly  from  an  oil  can  to  the  "  lubricated ?"  part  or  into  an 
oil  hole  which  is  supposed  to  conduct  the  oil  to  the  part.     To 
employ  human  labor  for  the  performance  of  a  duty  which  can 
so  easily  be  performed  automatically,  or  nearly  so,  is,  in  most 


SEC.  488]  STEAM-ENGINE  LUBRICATION  461 

cases,  wasteful.  Next,  the  tendency  on  the  part  of  the  human 
oiler  is  to  flood  each  bearing  with  oil  when  attending  to  it 
and  then  to  neglect  it  as  long  as  possible.  Such  attention 
results  in  a  great  waste  of  oil  and  no  great  reduction  in  bearing 
friction,  since  the  bearing  is  nearly  always  in  only  a  semi- 
lubricated  condition — it  is  lubricated  merely  by  what  oil 
has  remained  in  the  bearing. 

NOTE. — HAND  OILING  Is  SOMETIMES  SATISFACTORY  FOR  STEAM 
ENGINE  BEARINGS  which  have  very  limited  motion  and  small  bearing 
loads.  For  example,  it  is  frequently  used  for  valve  and  governor  mech- 
anisms, for  slow-speed  rocker  arms,  and  the  like.  For  high-speed  large- 
bearing-load  lubrication  it  is  extravagant  and  unsatisfactory. 

NOTE. — THE  OIL  FOR  A  HAND-OILING  SYSTEM  must  be  one  which  will 
not  readily  flow  out  of  the  bearing.  It  must  "cling"  to  the  bearing  sur- 
faces and  withstand  their  " squeezing"  action.  Hence,  it  is  essential 
that  it  have  a  high  viscosity  and  great  adhesion.  High  viscosity,  again, 
will  mean  great  fluid  friction  which  further  lessens  the  value  of  the 
lubrication.  High-viscosity  compounded  oils  (Sec.  483)  are  best  suited 
to  hand-feed  systems. 

488.  "Drop-Feed"  Lubrication  Of  External  Bearings  includes 
all  oiling  devices  which  provide  a  regular  feeding  of  oil,  drop 
by  drop,  to  the  bearings.  Drop-feed  oiling  provides  more 
uniform  lubrication  than  hand  oiling  but  has  some  disadvan- 
tages. Generally,  with  it  no  oil-purifying  apparatus  is  em- 
ployed and  the  oil  is  generally  used  once  and  then  wasted. 
Such  use  of  oil  usually  results  in  feeding  just  a  bare  minimum 
of  oil  to  the  bearings  and,  to  keep  down  the  oil  cost,  a  heavy 
oil  is  purchased  and  therefore  friction  is  not  reduced  to  a 
minimum.  Also,  drop-feed  oilers  require  constant  attention 
to  insure  that  they  do  not  run  empty.  They  also  feed  more 
oil  when  filled  to  the  top  than  when  nearly  drained.  See 
Table  483  for  recommended  oils  for  drop-feed  lubrication. 

NOTE. — DROP-FEED  OILERS  (Figs.  512  and  513)  ARE  MOUNTED 
directly  over  stationary  (and,  in  some  cases,  moving)  bearings.  Methods 
of  delivering  oil  from  oilers  to  moving  engine  bearings  will  be  discussed 
in  subsequent  sections. 

NOTE. — SHOULD  THE  SIGHT-FEED  BE  BROKEN  FROM  A  DROP-FEED 
OILER  IT  MAY  BE  REPAIRED  with  pipe  fittings  as  shown  in  Fig.  514. 
After  drilling  a  peep  hole,  H,  through  a  coupling,  C,  two  bushings,  B} 


462     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.   16 

are  screwed  firmly  into  it  and  the  glass,  G,  is  set  with  cement  or  putty. 
The  lower  end  of  the  original  oiler  may  readily  be  fitted  to  the  new  sight- 
feed  as  shown  in  Fig.  515. 


Snap 
/ 'Lever 


I-Side     View  H- S  eetional  View 

Fia.  512. — Typical  drop-feed  oil  cup  with  sight  feed.     (Lunkenheimer  Co.) 

489.  The  Suitable  Applications  For  Drop-Feed  Lubrication 
On  Steam  Engines  are  those  where  the  engine  is  not  sufficiently 
large  to  justify  the  cost  of  a  complete  splash  or  circulation 
oiling  system  or  where  the  engine  is  used  infrequently.  It  is 
seldom  that  this  system  is  used  to  the  exclusion  of  others  on 
engines  of  capacities  greater  than,  say,  25  h.p.  Often  on 
larger  engines,  even  the  largest,  this  system  is  employed  for 
the  slow-speed  light-load  bearings  such  as  the  wrist  plates, 
rocker  arms,  governor  spindles  and  the  like. 


SEC.  490] 


STEAM-ENGINE  LUBRICATION 


463 


490.  The  Bottle  Oiler  (Fig.  516),  although  not  widely  used 
on  steam  engines,  is  an  ingenious  device  and  gives  good  results 
when  properly  adjusted.  The  plunger,  C,  fits  loosely  in  the 
brass  tube,  A ,  so  that,  as  C  is  given  a  little  motion  up  and  down 
by  the  rotation  of  the  shaft,  oil  will  work  down  onto  the  shaft. 
Oilers  of  this  type  are  very  useful  on  shaft  bearings — particu- 


•  Exterior  View 


H-  Sectional  View 


FIG.  513. — Crank-pin  oiler  for  attachment  to  connecting  rod.  (The  valve  plunger, 
P,  rises  and  falls  as  the  crank  pin  rotates  thus  controlling  the  oil  feed.  With  the  engine 
stopped,  P  rests  against  the  seat  S  shutting  off  the  oil  flow.  American  Injector  Co.) 


larly  line  shafts — which  run  intermittently,  because,  due  to 
its  viscosity,  they  feed  no  oil  when  the  shafts  are  still.  They 
are  made  with  glass  bodies  so  that  the  oil  content  of  the  reser- 
voir is  visible  at  all  times.  Adjustment  of  oil-feed  can  only  be 
attained  by  changing  the  plunger  for  one  of  a  different  diameter. 
The  smaller  the  plunger  diameter,  as  compared  to  the  bore 


464    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE   [Div.  16 

of  the  tube  within  which  it  fits,  the  greater  will  be  the  rate  of 
oil-feed. 

491.  Ring-Oiled  Bearings  (Fig.  517),  although  seldom  found 
on  steam  engines,  are  very  effective  and  reliable.  The  bearing 
cap,  C,  is  cut  away,  for  a  small  portion  of  its  length,  to  allow 


:-  -Adjusting 
5crew 


.Coupling  Washer 

-Reducing  Bushing    \ 


Ho/e  Drifted  * :  -Reducing 

Through  Coup/ing      Bush/ng 

FIG.  514. — Improvised  sight  feed  for 
drop-feed  oiler.  (F.  W.  Bentley,  Jr., 
in  Power,  June  11,  1918.) 


FIG.  515. — Homemade  sight  feed  applied  to 
drop-feed  oiler. 


the  oiling  ring,  R,  to  ride  upon  the  shaft,  S,  as  shown.  As  R 
is  always  dipping  into  the  oil  in  the  reservoir,  A,  and  as  rotation 
of  S  will  cause  R  to  "ride"  it  and  thereby  also  revolve,  R 
will  continually  carry  oil  upward  onto  S.  A  liberal  quantity  of 
oil  is  thus  fed  to  the  bearing  whenever  the  shaft  rotates. 
Ring-oiled  bearings  require  attention  only  to  see  that  enough 
oil  is  within  the  reservoir  (some  oil  is  lost  by  leakage  and  evapo- 


SEC.  492] 


STEAM-ENGINE  LUBRICATION 


465 


ration).     A  periodic  renewal  of  the  oil  in  the  bearing  will 
prevent  the  accumulation  of  grit  and  damage  resulting  from  it. 


Cast-Iron         Excess  Oil      . 

Bearing  Ha/ves,   Sp/ashes      rifl/ng-Hole 


Drain 
Cock 


^Pedestal 


Ptunger 


I-  Cross  Section 


^'Babbitt-Metal    'Bronze  \ 

Lining  Oil         ', 

Ring    .' 

Oil  Reservoir 

n- Longitudinal 
Section 


FIG.  516. — Glass  bottle-oiler.        FIG.  517. — Typical  ring-oiled  bearing.      (The  spherical 

seat  makes  the  bearing  self -aligning.) 

492.  The  Splash  System  Of  External-Bearing  Lubrication, 

Fig.  518,  is  widely  used  on  modern  medium-  and  high-speed 
engines.     The  crank  disc,  B,  dips  into  the  oil  in  the  crank  case 


•$m®*i^ 

FIG.  518. — A  typical  splash-oiled  engine. 

to  a  depth  of  about  2  in.  and  throws  the  oil,  which  it  picks  up, 
onto  the  crosshead  guides,  C,  and  the  crosshead.  Some 
oil  is  collected  in  the  trough,  N,  from  which  it  is  led  by  pipes 

30 


466     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 

(Fig.  519)  to  the  main  bearings  and  to  the  eccentric.  Small 
quantities  of  water  will  work  their  way  into  the  crank  case 
(steam  which  leaks  through  the  packing  gland  and  then 
condenses)  and  must  be  removed.  This  may  be  done  auto- 
matically with  an  overflow  pipe  as  shown  at  L  in  Fig.  518. 
Frequently,  an  auxiliary  stuffing  box  is  placed  on  the  dividing 


0/7  Drops  Thrown  From 
Crank  Disc  By 
Centrifugal  F 


FIG.  519. — Section  through  splash-oiled  engine  at  shaft,  showing  oil  distribution  to 
bearings.     (Chandler  &  Taylor  Co.) 

wall,  D,  to  keep  water  out  of  the  crank  case.  In  vertical 
single-acting  engines  [with  large  crank  chambers  the  oil 
reservoir  is,  to  minimize  the  quantity  of  oil  required,  frequently 
filled  to  within  %  in.  of  the  under  side  of  the  crank  shaft 
with  water  upon  which  a  layer  of  oil  J£  to  J4  in.  thick  is  then 
poured.  The  dipping  of  the  connecting  rod  into  this  mixture 


SEC.  493] 


STEAM-ENGINE  LUBRICATION 


467 


forms  an  emulsion  which  is  then  splashed  to  the  several 
bearing  points.  Oils  for  splash  systems  are  given  in  Table 
485. 

493.  The  Gravity-Circulation  System  Of  External-Bearing 
Lubrication  (Figs.  520  and  521)  is  one  in  which  oil  is  supplied 
to  the  external  bearings  from  an  overhead  tank,  A,  and,  on 
leaving  the  bearings,  the  oil  is  collected  and  again  returned  to 
the  overhead  tank  by  a  pump,  B.  The  rate  of  oil-feed  to 
each  bearing  is  regulated  by  a  needle,  valve  in  a  sight-feed 


Main  - 

Bearing/ 

Crank-       Offer.  Cross  head-   \ 

Pin 
Oiler^ 


Gage  G/ 


•.•^y:-:--.:-*:*-^.-:*-;--"-'-  >-.'-",jV  <•»     .•:ar  "">:•' -"A.  a  •  a ••>,.»' '•  •. •^^A/^TV 
•.^••.•^;^»y^--\:-^'-^-'-:^*':'^ 


FIG.  520. — A  typical  gravity-circulation  lubrication  system  with  filter  at  the  lowest 

point. 


oiler  (Fig.  522).  The  chief  advantage  of  the  gravity-circula- 
tion system  is  that  it  provides  a  continuous  and  generous 
supply  of  oil  to  every  bearing.  Another  advantage  is  that  it 
lends  itself  so  readily  to  the  use  of  an  oil  filter,  C  (Fig.  520), 
which  insures  the  supplying  of  clean  oil  to  the  bearings  at  all 
times  and  permits  the  use  of  the  same  oil  for  an  indefinite 
length  of  time.  New  oil  need  be  added  only  to  make  up  for 
losses  by  leakage  and  evaporation.  Any  reasonable  arrange- 
ment of  filter  and  overhead  tank  may  be  adopted  to  satisfy 
building,  space  and  other  considerations. 


468     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 


EXAMPLES. — The  filter,  C,  may  be  so  located  that  the  dirty  oil  from 
the  bearings  flows  to  it  by  gravity,  as  in  Fig.  520.     Or,  the  filter  may  be 


Gravity     Ta  n  k 


Filtered   Oil'' 


Filtered 

Oil- 
Suction  Strainers'  *pan  Discharge 

FIG.  521. — Filtering-and-circulation  oil  system.     (S.  F.  Bowser  &  Co.,  Inc.) 

situated  above  A  and  discharge  by  gravity  into  A,  in  which  arrangement 
the  dirty  oil  is  pumped  from  a  collecting  basin  up  to  A.  A  third  plan  is 
to  locate  the  filter  at  any  level  and  pump  the  oil  to  and  from  it  by  separate 

Place  for 
Drop -Feed  Oiler,. 


HI-  F  lush    Plug 
Screw    in  Top 
When    Drop- Feed 
Oiler   is  Not  Used 


I -Exterior     View 


H-  Sectioned    View 


FIG.  522. — Four-window   sight-feed    oiler   for   gravity   oiling      system.     (Richardson- 

Phenix  Co.) 

pumps.  Fig.  521  shows  diagrammatically  the  oil-flow  in  the  system  of 
Fig.  520.  Oil  filters  will  be  discussed  in  following  sections.  Oils  for 
gravity-circulation  lubrication  systems  are  specified  in  Table  483, 


SEC.  494] 


STEAM-ENGINE  LUBRICATION 


469 


NOTE. — AN  INEXPENSIVE   GRAVITY-CIRCULATION  LUBRICATING  SYS- 
TEM WITH  HAND  PUMPS  is  shown  in  Fig.  523.     Tanks  A,  B,  C,  and  E 
can  have  any  shape.     F  and  G  are  hand  force-pumps.     D  is  the  oil 
filter.     Tanks  B  and  C  are  simply  to 
hold  supply  oil  for  A  and  D  and 
thereby  make  continuous  pumping 
unnecessary. 

494.  The  Force-Feed  Circu- 
lation System  Of  External- 
Bearing  Lubrication,  Fig.  524, 
is  one  in  which  oil  is  supplied 
to  the  external  bearings  by  a 
pump,  A}  under  a  pressure  of, 
say,  5  to  15  Ib.  per  sq.  in.  The 
oil  is  taken  from  the  reservoir, 
R,  in  the  crank  case  by  A  and 
delivered  through  pipes,  B,  to 
the  main  bearings.  Since  the 
crank  shaft  is  hollow,  the  oil 
is  led,  as  shown  from  the  main 
bearings  to  the  crank  pins  and 
eccentric.  It  is  then  conducted 
through  pipes,  C,  to  the  cross- 
head  pins.  Oil  which  leaves 
the  crosshead  splashes  onto  the 
guides  and  thence  falls  back 
into  the  reservoir.  An  adjust- 
able relief  valve,  not  shown, 
permits  by-passing  some  of  the 
oil  into  the  reservoir  as  it  is 
discharged  by  the  pump.  The 

.,„,,,,,  .  F  i  a.     523.  — A     simply-constructed 

Oil-teed  tO   the   bearings  Can  be   gravity-circulation    system.     (T.     G. 
increased  by  adjusting  the  relief    Thurston,  in  The  National  Engineer,  Feb., 

valve  to  maintain  a  higher  pres- 
sure at  the  pump  discharge.  As  the  bearings  become  worn,  a 
higher  pressure  is  necessary  to  keep  them  filled.  Also,  a  light 
oil  will  require  a  higher  pressure  than  a  heavy  oil.  Water, 
which  will  find  its  way  into  the  crank  case  from  the  cylin- 
der, must  be  drained  off  at  frequent  intervals.  A  scraper 


470    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 


gland,  D,  on  each  piston  and  valve  rod,  may  be  effectively 
used  to  keep  some  of  the  water  out  of  the  crank  chamber. 
See  Table  484  for  recommended  oils  for  force-feed  circulation 
systems. 


Low-Pressure 
Cylinder* 


High  -Pressure 
Cylinder, 


''Oil  'O//  ^-  Oil 

Pump     Resevoir       Level 

Fia.  524. — Compound  marine  engine  with  force-feed  lubrication. 

495.  The  Relative  Merits  Of  Automatic  Lubrication 
Systems  For  External  Bearings  may  be  briefly  stated  as 
follows:  (1)  Splash-oiling  systems  are  inexpensive  in  first  cost 
and  operate  very  satisfactorily  on  engines  of  speeds  of  200 
r.p.m.  or  more.  The  oil  must  be  periodically  renewed  but, 
if  filtered,  can  be  used  over  and  over.  (2)  Gravity  circulation 
systems  afford  a  copius  supply  of  oil  to  each  bearing,  are  simple 
and  easy  to  operate,  and  can  be  fitted  to  any  engine.  The 
flow  of  oil  to  each  bearing  is  known  and  is  readily  adjustable. 


SEC.  496] 


STEAM-ENGINE  LUBRICATION 


471 


(3)  Force-feed  circulation  systems  are  very  positive — that  is, 
the  oil  supplied  to  a  bearing  is  more  apt,  than  in  the  first  two 
systems  discussed,  to  actually  enter  between  the  bearing 
surfaces.  On  the  other  hand,  the  oil-feed  to  each  bearing  is 
unknown,  and  if,  for  any  reason,  a  pipe  or  passage  should 
become  clogged  this  may  only  be  evidenced  after  serious 
damage  to  the  bearing.  In  view  of  the  above,  the  gravity 
circulation  system  is  becoming  very  widely  used  for  modern 
slow-speed  engines,  whereas  the  splash  system  is  in  general 
use  on  higher-speed  engines. 

496.  Methods  Of  Supplying  Oil  To  Moving  Bearings  Of 
Medium-  And   Slow-Speed   Engines  are  numerous  and  are 


Drop- 
(Oil  Cup 


'rank 


,  -  -Supported 
^WW  Floor 

FIG.  525. —  "Banjo"    crank-pin    oiler   for 
side-crank  engine. 


Sight-Feed 
Drop-Oiler-,^ 


<- -Crank  Disc 


Weight' 
"-Crank  Pin 


FIG.  526.  —  Nugent  crank-pin  oiler. 


usually  such  that  an  engine  need  not  be  shut  down  to  adjust 
the  oil  feed  or,  where  necessary,  to  fill  the  oilers.  In  the  illus- 
trations which  accompany  this  section,  hand-supplied  drop- 
feed  oilers  are  shown.  But  oil  may  be  conducted  to  these 
oil  cups  by  a  gravity  oiling  system  if  such  is  available.  In 
the  crank-pin  oiler  (Fig.  525),  which  is  widely  used,  oil  is  fed 


472    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE   [Div.  16 


from  the  cup  to  tube  F,  which  delivers  it  to  the  hollow  ball 
D.     Tube  C  is  fastened  securely  to  D  and  to  the  crank  pin, 


.-Cross head 


Fe/t 

Wr'ck 

(Wipes  Oil. 
from  Oiler) 


'Ho/low 
Space 
(Oil  from 
Drop -Feed 
Oiler  Drips 
in  Here  ) 


Crosshead'  Splash  Guard' 

I-Sid»View  H- Section 

FIG.  527. — Method  of  using  wiper  cup 
in  oiling  crosshead  pin 


.  ~,~.,nping  Screw 
(Top  Part  TMay 
^\  be  Rotated  info 
r  '  any  Position 
and  there 

Clamped) 

Standard  Pipe 

Threads '' 
I-Wiper  Cup  H-  Drip  Boat 

FIG.  528. — Oil  collecting  devices.    (Sher- 
wood Mfg.  Co.) 


I- End    View  H-Side  View 

FIG.  529. — Crosshead-pin  telescopic  oiler.      (Richardson-Phenix  Co.) 

B.  and  rotates  with  B.  Oil,  dripping  from  F  to  D,  is  carried 
through  C  by  centrifugal  force  and  enters  B  where  it  lubricates 
the  bearing.  A  similar  device  is  one  (Fig.  526)  in  which  the 


SEC.  496] 


S  TEA  M-ENGINE  L  UBRICA  TION 


473 


oil  cup,  instead  of  being  mounted  on  a  rigid  support,  is  held 
upright  by  a  weighted  pendulum  to  which  it  is  attached; 
this  is  not  suited  to  the  gravity  system.  The  revolving  crank, 
B,  receives  oil  from  tube  C  and  delivers  it  to  the  crank  pin. 
The  usual  method  of  oiling  the  crosshead  guides  (Fig.  527) 
is  to  drop  oil  from  the  cup,  A,  onto  the  upper  shoe.  Drips 
from  A  and  from  the  pin  lubricate  the  lower  shoe,  being 
retained  by  splash  guards,  D,  at  each  end  of  the  guide. 


Engine 
Cylinder 


-  ~Cros$head 


FIG.  530. — Vertical  engine  equipped  with  swing  joints  for  supplying  oil  to  crank  and 

crosshead  pins. 


NOTE. — ECCENTRICS  AND  CROSSHEAD  PINS  ARE  FED  BY  WIPER  CUPS 
OR  TELESCOPIC  TUBES  (Figs.  527,  528  and  529).  The  wiper  cup,  C 
(Fig.  527),  supplies  the  crosshead  pin  with  oil  from  B.  Fig:  528  shows  a 
wiper  cup  and  a  drip  boat  which  is  used  as  a  wiper  cup  for  feeding  oil  to 
eccentrics.  Telescopic  tubes  (Fig.  529)  are  more  effective  for  cross- 
head  pin  and  eccentric  oiling  but  are  not  applicable  to  crosshead  pins 
of  vertical  engines.  On  the  other  hand,  the  swing-joint  arrangement  of 
Fig.  530  is  especially  suited  to  vertical  engines.  Swing-joint  and  tele- 
scopic oilers  cannot  be  used  effectively  on  high-speed  engines  because 
of  the  liability  of  their  becoming  disarranged  or  broken  when  operating 
at  high  speeds. 


474    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 


497.  The  Operation  Of  A  Good  Oil  Purifier  Or  Filter  (Figs. 
531,  532  and  533)  usually  comprises  three  separate  processes : 

(1)  Screening  is  intended  to  remove  the  coarser  impurities  and 
relieve  the  following  processes  of  as  much  burden  as  is  feasible. 

(2)  Precipitation  consists  of  allowing  the  finer  impurities  of 
higher  specific  gravity  than  the  oil — such  as  fine  metallic 
wearings  and  water — to  settle  out  from  the  oil.     Precipitation 
is   often   accelerated    by   heating  the  oil,  thus  lowering  its 
viscosity  and  allowing  the  impurities  to  pass  more  freely 
through  it.     Separated  water  should  be  removed  by  an  auto- 
matic   overflow.     (3)    Filtration   is  intended  to  remove  the 
very  finest  floating  impurities  in  the  oil — those  which  have 
not  been  removed  in  either  the  screen  or  the  precipitation 
chamber. 

NOTE. — PASSING  THE  OIL  THROUGH  WATER  DOES  NOT  REMOVE 
IMPURITIES  although  some  engineers  try  to  filter  oil  in  this  way.  The 
oil  rises  through  the  water  in  drops  from  which  the  impurities  cannot  be 
removed  no  matter  how  hot  the  water  mav  be. 


,'lnner  Can 
Filled  with 
Dirfy  Oil 


498.  The  Filtering  Materials 
Used  In  Oil  Filters  are  various. 
Most  small  filters  employ,  as  a 
filtering  medium,  cotton  waste, 
sawdust,  wool,  or  other  loose 
material,  but  in  large  filters 
cloth  is  universally  used.  Even 
for  small  filters,  cloth  in  the 
form  of  a  simple  bag  is  pref- 
erable to  loose  material. 
Loose  material,  unless  well 
packed,  will  allow  channels 

FIG.  531. — A  simply-constructed  oil     J 

through  which  the  oil  will  pass 
without  being  filtered.  If  tightly 
packed,  such  material  reduces  the  filter's  capacity  to  possibly 
1  or  2  gal.  per  day.  Filter  cloth  should  preferably  be 
arranged  so  that  the  impurities  will  fall  away  from  the  cloth 
as  they  collect.  With  horizontal  filter  surfaces,  the  oil 
should  flow  upward  through  the  cloth  which  should  have  a 
pan  under  it  to  prevent  the  impurities  falling  on  the  cloth 
beneath.  Vertical  filter  surfaces  are  preferable  to  those 


filter.      (J.  C.  Kahl,  in^Southern  En 
gineer,  Sept.,  1910.) 


SEC.  498J 


STEAM-ENGINE  LUBRICATION 


475 


horizontal  surfaces  through  which  the  oil  flows  downward 
through  the  cloth,  as  the  latter  are  apt  to  become  clogged  with 
impurities.  It  is  also  desirable  to  have  the  two  sides  of  the 

Pour  Dirty  Oil  In  Here-. 


Wire-Netting 
Stralner- 


'aste 


Wire- 
Netting 
Strainer^ 


FIG.  532. — A  simply-constructed  improvised  oil  filter.     (E.  Grossenbacher,  in  Power, 

Mar.  9,  1920.) 

filter  surface  exposed  to  the  same  difference  in  oil  pressure  at 
all  points.     If  the  oil  at  the  bottom  of  a  filtering  surface  is 


476    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 


forced  through  at  a  greater  pressure  than  at  the  top,  the  cloth 
at  the  top  will  pass  less  oil  than  that  at  the  bottom,  and, 
furthermore,  impurities  may  be  forced  through  at  the  bottom 
by  the  greater  pressure.  In  some  small  niters  the  oil  is  filtered 
by  syphoning  it  through  felt  strips. 

NOTE.  —  IMPROVISED  OIL  FILTERS  MAY  BE  CONSTRUCTED  READILY. 
Fig.  531  shows  such  a  filter  which  employs  felt  strips  as  the  filtering 
material.  It  gives  very  satisfactory  results  as  only  clean  dry  oil  will 


Dirty  Oil 


screen 


Thermometer\\  n — 14/\  I  /  \\Trc 

H  L  l^  w.L. 


Clean  Oil  Outlet-' 
FIG.  533. — Oil  filter.      (Richardson-Phenix  Co. ) 

syphon  over  the  top  of  the  inner  can.  Fig.  532  shows  a  homemade  filter 
employing  a  loose  filter-material  and  made  of  barrel  and  can  parts. 
In  using  such  a  filter  care  must  be  taken  that  the  material  is  closely 
packed  especially  at  the  outer  edges  and  that  water  does  not  collect  in 
barrel  B  to  a  level  higher  than  the  bottom  of  cone  C,  as  this  would 
permit  water  to  enter  the  second  compartment. 

499.  Oil  Purifiers,  Usually  Called  Filters,  Are  Manufactured 

in  capacities  up  to  3800  gal.  per  min.  In  the  Peterson  oil 
filter  (Figs.  533  and  534)  oil  is  poured  in  and  screened  at  A, 
and  after  passing  over  the  heating  coils,  B,  flows  down  the 
tube,  C,  striking  deflector,  D.  From  the  bottom,  the  oil 


SEC.  500] 


STEAM-ENGINE  LUBRICATION 


477 


flows  slowly  upward  over  the  several  trays,  T,  gradually  losing 
its  water  and  heavy  impurities,  and  finally  passes  through  G 
into  the  filter  compartment,  shown  in  Fig.  533.  The  sepa- 
rated water  flows  to  the  bottom  of  the  precipitation  chamber 
through  the  funnels  around  C  and  through  the  tube,  E.  It 
is  automatically  discharged  through  the  overflow  pipe,  P, 
which  is  adjustable  in  height  for  different  oils.  In  the  filtra- 
tion compartment,  H  (Fig.  533),  the  oil  flows  through  the  filter 


Screen --V. 


^-Dirty-Oil 
Inlet 


Deflector' 


FIG.  534. — Section  through  precipitation  compartment  of  the  oil  filter  shown  in  Fig.  533. 

cloth,  which  is  supported  on  frames,  J,  from  the  outside  to 
the  inside.  Impurities  collect  on  the  filter  surfaces  and  fall 
to  the  bottom  of  H.  The  clean  oil  flows  from  the  inside  of 
frames ,  /,  through  valves ,  K,  into  the  clean  oil  compartment,  L. 

NOTE. — As  the  filter  frames,  J,  are  always  full  of  oil,  there  exists  the 
same  difference  of  pressure  between  outside  and  inside  of  the  cloth  at  all 
points  on  the  cloth.  This  pressure  is  shown  by  the  height  of  oil  in  the 
head  gage,  R.  The  clean  oil  is  taken  out  through  pipe  M . 

500.  In  A  Bowser  Oil  Filtering  Outfit  (Fig.  535),  dirty  oil 
is  introduced  and  screened  at  A  and  collects  in  the  refining 
and  purifying  chamber,  P,  where  it  is  heated  by  the  steam 


478    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 


coil  and  then  passes  up  over  the  trays,  B.  The  oil  then  over- 
flows through  the  regulating  valve,  E,  to  the  filter  bag,  C 
through  which  it  passes  to  D,  the  clean  oil  storage  tank. 
Another  Bowser  outfit  is  that  shown  diagram matically  in  Fig. 
521.  The  filter  cloths  in  this  outfit  are  placed  in  the  hori- 
zontal position  in  the  filter  pan  and  allow  the  oil  to  pass 
upward  through  them.  Pans  (not  shown),  between  the 
layers  of  filter  cloth,  catch  the  impurities  as  they  fall  from  the 
cloth  surface. 

501.  The  Sub ject  Of  Internal- 
Bearing  Lubrication  may  be  con- 
veniently treated  under  three 
headings.  (Internal  bearings  are 
defined  in  Sec.  486.)  (1)  Nature 
of  the  lubricant.  Engines  oper- 


Removable 
Cap  -  -  . 


Regu/ating  Va/ve^ 

"\  Filtering 

Removab/e  fining  And     \Chamberand 
,  Stnr/ntr      Pur/ fymg  Chamber  \  Reservoir 


O/7  Reservoir-- 


•Strainer 


FIG.  535.  —  Oil    filtering    outfit.     (S.    F. 
Bowser  &  Co.,  Inc.) 


FIG.  536. — Typical  hand  push  pump 
with  glass  body.  (Detroit  Lubricator 
Co.) 


ating  on  wet  steam  require  a  lubricant  which  is  not 
readily  washed  from  the  cylinder  walls.  Engines  operat- 
ing on  superheated  steam  require  a  lubricant  which  will  not 
carbonize  or  become  too  thin  at  the  high  superheat  tempera- 
ture; see  Fig.  511.  (2)  Appliance  used  to  feed  the  lubricant. 
This  can  be  a  hand  pump  (Fig.  536),  a  hydrostatic  lubricator 
(Fig.  541),  or  a  mechanical  force-feed  lubricator  (Fig.  544). 
These  appliances  will  be  discussed  in  following  sections.  (3) 
Manner  of  introducing  the  lubricant  to  the  bearings,  discussed 
below. 

502.  The  Most  Preferable  Manner  Of  Introducing  Cylinder 
Oil  is  to  mix  it  with  the  supply  steam  as  the  steam  approaches 


SEC.  502] 


STEAM-ENGINE  LUBRICATION 


479 


the  engine.  Unless  the  engine  builders  recommend  some 
other  scheme,  the  oil  should  be  fed  into  the  steam  pipe  above 
the  throttle  valve  and  thoroughly  atomized  before  it  reaches 
the  cylinder.  Feeding  the  oil  through  a  pipe  which  does  not 
extend  into  the  interior  of  the  steam  pipe  is  apt  to  allow  the 
oil  to  flow  down  the  inner  surface  of  the  steam  pipe  without  its 
being  well  mixed  with  the  steam.  A  slotted  pipe  extending  a 
"spoon-shaped"  end  well  into  the  steam  pipe  (Fig.  537) 
will  cause  the  steam  to  "spray"  the  oil  through  the  slots  and 


Cap 


FIG.  537.  —  Atomizer  for  internal 
lubrication  of  steam  engines.  (This 
arrangement  may  be  used  with  any 
internal-lubricating  apparatus.) 


FIG.  538. — Gravity  valve  or  oil  check 
valve.  (MacCord  Mfg.  Co.  Weighted 
valve  A  is  raised  from  its  seat  by  oil 
which  enters  B  and  flows  out  at  O.  But 
oil  flow  in  the  opposite  direction  is  pre- 
vented by  A.) 


thus  to  thoroughly  atomize  it.  A  check  valve  should  be  placed 
as  shown  to  insure  a  steady  flow  of  oil.  Some  provision 
should  be  made  that  a  vacuum  in  the  steam  pipe  will  not  draw 
the  oil  out  of  the  feed  pipe.  A  gravity  valve  (Fig.  538)  or  a 
suitable  spring-loaded  check  valve  will  provide  this  assurance. 

NOTE. — FLAKE  GRAPHITE  Is  SOMETIMES  FED  To  THE  VALVES  AND 
CYLINDER,  the  object  being  to  have  the  graphite  "cake"  on  to  the 
rubbing  surfaces  and  glaze  them,  thus  reducing  the  amount  of  oil  neces- 
sary for  good  lubrication.  Very  small  quantities  of  graphite,  usually 
1  to  3  per  cent,  by  weight  of  the  oil  supplied,  are  fed,  generally  through 


480    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 


a  separate  graphite  feeder,  Fig.  539,  and  directly  to  the  steam  chest. 
Some  force-feed  lubricators  will  handle  a  mixture  of  graphite  and  oil.  A 
separate  graphite  feeder  is  then  unnecessary. 

NOTE. — LUBRICATION  OF  THE  STUFFING  BOXES  is  usually  accomplished 
by  the  oil  introduced  with  the  steam.  Wherever  metallic  packing  is 
used,  however,  it  is  customary  to  supply  oil  directly  to  the  stuffing  boxes 
through  separate  oil-feed  pipes. 


503.  Feeding  Oil  To  Internal 
Bearings  By  Hand  is  scarcely  ever 
attempted  except  as  a  stand-by 
arrangement  for  use  if  the  custo- 
mary method  of  feeding  becomes 
inoperative.  A  hand  oil  pump 
(Figs.  536  and  540)  should,  there- 
fore, be  placed  on  the  cylinder  oil- 
supply  pipe  of  every  engine  and  so 
arranged  that  it  can  be  brought 
into  service  on  very  short  notice. 


Shut-Off 
Valve 


FIG.  539. —  "Auxiliary"  graphite 
feeder  (Lunkenheimer  Co.)  for  attach- 
ment to  steam  chest. 


^-Standard 
Pipe  Thread 


FIG.  540. — Lever-handle  oil  pump, 
heimer  Co.) 


(Lunken- 


504.  The  Principle  Of  The  Hydrostatic  Lubricator  (Fig. 
541)  is  a  simple  one.  The  pipe,  A,  is  connected  into  the 
engine  steam-supply  pipe,  18  in.  or  more  above  the  lubricator, 
and  is  also  connected  to  a  condenser,  C.  In  pipe  A  and  in  C 
the  steam  which  enters  at  A  is  condensed  into  water,  which, 
when  valve  B  is  open,  can  flow  through  pipe  D,  down  into  the 


SEC.  504^ 


STEAM-ENGINE  LUBRICATION 


481 


bottom  of  the  oil  reservoir,  E.  This  incoming  water  displaces 
oil  which  is  forced  out  through  pipe  F  and  through  the  adjust- 
ing valve,  F,  which  is  simply  for  regulating  the  feed.  The  oil 
then  rises  through  the  water  in  the  sight-feed  glass,  S,  and 
enters  the  steam  pipe,  R,  through  the  delivery  pipe,  L.  The 
gage  glass,  G,  shows  the  level  of  the  oil  in  the  reservoir.  The 
oil  is  forced  into  R  only  by  the  column  of  water  in  and  above  C. 


Feed  Adjusting     Drain  ? 
Valve  cock'' 


FIG.  541. — Hydrostatic  lubricator. 


Nipple-' 

Coup/ ing  — > 

Bushing •-,. 

Drain 
Cock-... 


FIG.  542. — Hydrostatic  lubricator  con- 
structed of  pipe  fittings.  (A.  O.  Stone,  in 
Power  House,  Jan.  20,  1920.) 


The  lubricator  must  be  started  and  stopped  with  the  engine, 
otherwise  it  would  continue  feeding  and  thereby  waste  oil. 
The  rate  of  oil-feed  depends  on  the  viscosity  of  the  oil  and 
will,  therefore,  change  with  different  room  temperatures 
and  each  time  the  lubricator  is  refilled. 

NOTE. — AN  EMERGENCY  HYDROSTATIC  LUBRICATOR  READILY  MADE 
OF  PIPE  FITTINGS  is  shown  in  Fig.  542.  Regulation  of  oil-feed  is  attained 
by  adjustment  of  the  valve,  A.  It  is  evident  that  such  a  lubricator; 
since  it  has  no  sight-feed  glass,  is  not  at  all  reliable.  It  is  useful  only  as 

an  emergency  device.     To  equip  this  lubricator  with  a  sight  glass  would 
31 


482     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 

probably  involve  a  cost  such  that  it  would  be  preferable  to  purchase  a 
manufactured  lubricator. 

505.  The  Care  And  Operation  Of  Hydrostatic  Lubricators 
are  simple.  In  filling  the  lubricator  valves  B  and  V,  Fig. 
541,  are  closed;  then  drain  cock  X  and  plug  P  are  opened. 
After  all  water  has  drained  out  of  E,  X  is  closed  and  fresh  oil 
is  poured  into  P.  In  cold  weather  it  may  be  necessary  to  heat 
the  oil  to  sufficiently  reduce  its  viscosity  that  it  will  readily 
flow  into  the  reservoir.  Should  the  condenser,  C,  by  any 


FIG.  543. — Scheme  whereby  a  hand  oil  pump  may  be  used  for  filling  a  hydrostatic 
lubricator.  (W.  R.  Weiss  in  Power,  Apr.  19,  1921.  By  connecting  the  pipe  from  P  to 
the  lubricator  at  C  instead  of  at  the  bottom,  an  arrangement  is  secured  with  which  the 
operation  of  the  lubricator  need  not  be  stopped  to  fill  it.  Pumping  oil  into  the  lubricator 
will  then  force  the  water  out  through  the  steam  pipe  whence  it  will  flow  to  the  engine  with 
the  supply  steam.  If  the  pumping  is  done  slowly,  this  small  amount  of  water  will  not 
harm  the  engine.) 

chance  be  drained  of  its  water,  sufficient  time  must  be 
allowed  for  it  to  fill  before  opening  B  to  the  oil.  Otherwise, 
steam  would  enter  the  oil  and  cause  " churning"  in  the  sight- 
feed  glass.  The  only  remedy  for  churning  is  to  completely 
empty  the  lubricator,  cool  it,  fill  afresh,  and  wait  for  the 
condenser  to  fill  with  water.  If  the  sight-feed  glass  gets 
smeared  with  oil,  the  cause  may  be  that  the  drops  are  too 


SEC.  506]  STEAM-ENGINE  LUBRICATION  483 

large  for  the  bore  of  the  glass  tube.  This  can  usually  be 
remedied  in  one  of  three  ways:  (1)  Fit  a  larger  diameter  glass. 
(2)  Solder  a  wire  on  to  the  nipple  (at  which  the  drops  form)  to 
guide  the  oil  drops  centrally  up  the  tube.  (3)  Fill  the  sight- 
glass  with  salt  water  or  glycerine.  The  heavier  specific  gravity 
of  these  liquids  will  cause  the  oil  to  rise  in  smaller  drops  which 
will  not  touch  the  glass. 

NOTE. — LEAKAGES  OF  JOINTS  OR  PACKING  IN  HYDROSTATIC  LUBRI- 
CATORS MUST  BE  AVOIDED,  because  the  lubricators  are  very  sensitive 
and  leaks  are  sure  to  interfere  with  their  operation. 

NOTE. — A  METHOD  OF  FILLING  A  HYDROSTATIC  LUBRICATOR  WITH 
A  HAND  OIL  PUMP  is  shown  in  Fig.  543,  where  an  additional  pet-cock, 
C,  is  shown  mounted  at  the  top  of  the  gage  glass.  To  refill  the 
lubricator,  L,  it  is  first  shut  off  in  the  usual  manner  by  closing  valves 
B  and  V.  Cocks  C  and  E  and  valve  D  are  then  opened,  allowing  the 
water  to  drain  from  the  lubricator.  E  is  then  closed  and  oil  is  pumped 
from  P  to  L,  after  which  D  and  C  are  again  closed.  The  lubricator  is 
then  ready  for  service. 

506.  To   Prevent   Trouble   With  Hydrostatic  Lubricators 

it  is  necessary  to  use  only  oil  of  good  quality  and  to  be  sure 
that  it  is  absolutely  clean  and  free  of  all  foreign  substances. 
It  is  well  to  strain  all  of  the  oil  used  and  to  keep  it  well  protected. 
Sometimes  a  lubricator  cannot  work  because  some  of  its  small 
passages  have  become  clogged  with  dirt  from  the  oil.  It  is 
good  practice  to  occasionally  empty  the  lubricator  and  blow 
steam  through  it  so  as  to  thoroughly  clean  out  any  dirt  or  sedi- 
ment that  may  have  lodged  in  the  small  tubes  or  passages. 

NOTE. — THE  WATER  FEED  VALVE  OF  A  HYDROSTATIC  LUBRICATOR 
SHOULD  BE  LEFT  OPEN  WHEN  THE  ENGINE  Is  SHUT  DOWN,  as  during  the 
noon  hour,  and  when  the  oil  regulating  valve  is  closed.  The  lubricator 
being  connected  above  the  engine  throttle  valve,  steam  enters  the  support 
arm  and  heats  the  oil  in  the  body  of  the  lubricator  while  the  throttle  is 
closed  as  well  as  while  open.  This  heat  causes  the  oil  in  the  lubricator 
to  expand.  If  the  water  feed  valve  is  left  open  it  acts  as  a  vent,  and 
some  of  the  water  in  the  bottom  of  the  lubricator  body  will  be 
forced  up  into  the  condenser.  If  the  oil  regulating  valve  and  water  feed 
are  both  shut,  there  will  be  no  outlet  for  the  expanding  oil  which  may 
then  exert  such  a  pressure  on  the  body  as  to  cause  it  to  bulge. 

507.  Mechanical  Force-Feed   Lubricators    (Figs.   544  and 
545)  are  coming  into  extensive  use  for  internal  lubrication  of 
steam  engines.     In  general,  they  are  preferable  to  the  hydro- 


484     STEAM  ENGINE  PRINCIPLES  AND  PRACTICE    [Div.  16 


static  lubricators  because  they  are  more  positive  in  operation 
and  furthermore  they  can  be  arranged  to  automatically  start 
and  stop  with  the  engine.  A  great  number  of  different  kinds 


Ratchet 
Wheel-. 


,  Crank 

,( Feed- 
-' I  Adjusting 
'  Screws 


Connecting 
Roe/-. 


Heating  / 
Connection 

FIG.  544. — Exterior  view  of  single-feed,  metal-body,  force-feed  pump.     (Hills-McCanna 

Co.) 

are  on  the  market.     Most  of  them  are  very  satisfactory. 
In  the  one  shown  (Figs.  544  and  545),  the  connecting  rod,  C, 


•Feed- 
Adjusting 
Screws 


FIG.  545. — Section  through  force-feed  lubricator.     (Hills-McCanna  Co.) 

is  driven  from  some  part  of  the  engine  which  has  a  reciprocat- 
ing motion.  The  rachet  wheel,  R,  transforms  this  motion 
into  rotation  of  the  crank  shaft,  S,  which  again  imparts  recipro- 


SEC.  5tf8]  STEAM-ENGINE  LUBRICATION  485 

eating  motion  to  the  plunger,  A .  On  the  upward  stroke  of  A , 
oil  is  drawn  up  from  the  reservoir,  E,  (Fig.  545),  through  pipe 
F  into  the  displacement  chamber,  D.  From  D  it  is  forced  on 
the  downward  stroke  of  A,  past  the  sight  glass,  G  and  out 
through  a  pipe  attached  at  /,  to  the  engine.  Adjustment  of 
feed  is  accomplished  by:  (1)  Varying  the  amount  of  movement 
of  the  connecting  rod,  C.  (2)  Varying  the  stroke  of  the 
plunger,  A,  by  the  screws,  J. 

NOTE. — MULTIPLE-FEED  MECHANICAL  LUBRICATORS  are  useful  for 
supplying  oil  to  more  than  one  point.  In  compound  engines  a  multiple- 
feed  lubricator  can  be  employed  to  furnish  a  separate  supply  of  oil  to 
each  cylinder.  A  separate  feed  is  also  used  to  feed  each  stuffing  box 
which  is  to  be  oiled.  The  number  of  feeds  may  be  sufficient  to  supply 
every  need  of  an  entire  plant  with  one  lubricator,  in  which  event  the 
lubricator  is  motor-  or  steam-driven  and  the  feed  to  each  delivery  point 
must  be  started  and  stopped  by  an  attendant. 

NOTE. — IN  INSTALLING  FORCE-FEED  LUBRICATORS,  the  lubricator  may 
be  mounted  on  any  convenient  place  on  the  engine.  The  engine  builder 
or  engineer  will  designate  the  most  advantageous  location.  Installation 
should  be  made  so  that  the  sight  feeds  and  filler  plugs  are  in  full  view  of 
the  engineer.  The  ratchet  arm  can  be  driven  by  any  reciprocating 
motion  of  the  engine.  Always  use  pipe  free  from  rust.  Before  connect- 
ing up  the  valve,  make  sure  that  the  lubricator  is  clean  of  all  foreign 
matter  and  fill  the  lubricator  reservoir  with  oil.  Work  the  operating 
lever  by  hand  to  fill  the  oil  pipe  until  it  overflows.  In  this  way  the  oper- 
ator will  know  that  the  pipe  line  is  clear. 

508.  The  Proportional  Lubricator  Is  A  Modified  Hydro- 
static Lubricator  and  is  intended  to  furnish  internal  lubrication 
for  an  entire  plant;  see  Fig.  546.  A  reducing  and  enlarging 
(venturi),  section,  A,  is  placed  in  the  main  steam  pipe  from 
the  boiler.  The  lubricator  is  installed  to  deliver  oil  at  the 
reduced  section,  A.  The  condenser,  C,  however,  is  connected 
to  the  main  portion,  B,  of  the  steam  pipe.  As  steam  flows 
through  the  steam  pipe,  the  pressure  at  A  will  fall  below  that 
at  B,  due  to  the  velocity  of  the  steam.  The  greater  the  velocity 
of  the  steam,  the  greater  will  be  the  pressure  difference 
between  points  A  and  B.  This  difference  of  pressure  is 
utilized,  in  addition  to  the  difference  in  specific  gravity  of  the 
water  in  C  and  the  oil  in  F,  to  force  oil  from  the  lubricator 
through  the  needle  valve,  D.  Thus,  the  oil-feed  will  vary 


486    STEAM  ENGINE  PRINCIPLES  AND  PRACTICE   [Div.  16 

with  the  velocity  of  the  steam  in  the  main  pipe.  This  lubri- 
cator has  the  disadvantages  of  all  hydrostatic  lubricators 
and  besides,  unless  the  check  valve,  E,  is  properly  spring- 
loaded,  it  may  feed  oil  when  no  steam  is  flowing  in  A. 


~Feed-ActJu$  ting 
Va/ve 


•Sfancf 
FIG.  546. — Meyeringh  proportional  lubricator.     (Oil  Well  Supply  Co.,  Pittsburgh.) 


QUESTIONS  ON  DIVISION  16 

1.  What  is  the  primary  purpose  of  lubrication? 

2.  Define  friction. 

3.  Explain  rolling  friction. 

4.  Explain  sliding  friction. 

5.  Explain  fluid  friction. 

6.  What  happens  when  a  fluid  is  introduced  between  two  sliding  susfaces? 

7.  Define  body  as  applied  to  oils. 


SEC.  508]  STEAM-ENGINE  LUBRICATION  487 

8.  Define  viscosity  and  explain  with  a  sketch  how  it  is  measured. 

9.  What  does  the  viscosity  of  an  oil  determine? 

10.  Does  the  viscosity  of  an  oil  ever  change? 

11.  Explain  the  use  of  solid  lubricants. 

12.  Name  some  substances  which  are  solid  lubricants. 

13.  What  are  semi-solid  lubricants  and  what  are  their  use? 

14.  Name  three  general  classifications  of  oils  (classified  as  to  source  of  supply)  and 
explain  the  properties  of  each.  , 

15.  How  is  the  specific  gravity  of  an  oil  measured  and  what  does  it  indicate? 

16.  At  what  temperatures  are  oil  viscosities  usually  measured? 

17.  Define  flash  point,  fire  point,  and  chill  point. 

18.  How  are  the  above  points  used  in  the  selection  of  an  oil? 

19.  What  are  the  mechanical  conditions  of  a  bearing  and  how  do  they  affect  the  choice 
of  an  oil? 

20.  How  does  the  lubricating  system  which  is  used  in  an  installation  affect  the  selection 
of  an  oil  for  it? 

21.  What  are  deposits  in  oils  caused  by? 

22.  State  the  principal  properties  of  circulation  oils. 

23.  State  the  principal  properties  of  cylinder  oils. 

24.  What  are  the  external  and  internal  bearings  of  a  steam  engine? 

25.  Define  automatic  and  non-automatic  lubrication  of  external  bearings. 

26.  Discuss  the  lubrication  of  external  bearings  by  hand? 

27.  Discuss  drop-feed  lubrication. 

28.  What  is  the  bottle  oiler  and  how  does  it  function?     Explain  with  a  sketch. 

29.  Describe  and,  using  a  sketch,  discuss  ring-oiled  bearings. 

30.  What  are  the  applications  of  drop-feed  oiling? 

31.  Describe  and  discuss  splash  oiling. 

32.  Draw  a  diagram  of  a  gravity-circulation  oiling  system  and  discuss  its  merits. 

33.  Describe  and  discuss  the  force-feed  circulation  system  of  bearing  lubrication. 

34.  What  are  the  relative  merits  of  the  three  systems  of  Questions  31  to  33? 

35.  Enumerate  the  methods  of  supplying  oil  to  moving  engine  bearings  and  describe 
each. 

36.  Describe,  with  a  diagrammatic  sketch,  the  operation  of  a  good  oil  purifier. 

37.  How  should  oil  flow  through  cloth  filter  surfaces?    ' 

38.  How  can  water  be  automatically  removed  from  a  mixture  of  oil  and  water? 

39.  How  should  oil  be  introduced  to  an  engine  for  its  internal-bearing  lubrication? 

40.  How  may  graphite  be  introduced  to  the  internal  bearings? 

41.  How  are  the  stuffing  boxes  lubricated? 

42.  What  is  the  field  of  hand  oil-pumps? 

43.  Draw  a  sketch  and  with  it  discuss  the  principle  of  the  hydrostatic  lubricator. 

44.  Using  the  sketch  of  Question  43  show  how  a  hydrostatic  lubricator  is  refilled. 

45.  What  troubles  are  to  be  guarded  against  in  using  hydrostatic  lubricators  and  how 
are  they  avoided? 

46.  Describe  the  operation  of  a  mechanical  force-feed  lubricator.     Make  a  sketch  and 
tell  how  to  install  a  mechanical  force-feed  lubricator. 

47.  What  is  the  principle  of  the  proportional  lubricator? 


APPENDIX 
SOLUTIONS  TO  PROBLEMS 

The  Following  Solutions  To  The  Problems,  which  have  been 
presented  at  the  ends  of  the  various  divisions  throughout  the 
book,  are  included  to  assist  the  student.  These  solutions  should 
be  referred  to  only  after  the  reader  has  made  an  earnest  effort 
to  solve,  without  assistance,  the  problem  which  is  under  consid- 
eration. If  used  in  this  way,  these  solutions  may  constitute 
a  material  aid.  But  if  the  reader  refers  to  this  appendix 
before  he  has  made  an  honest  effort  to  work  out  his  own  solu- 
tion, then  the  material  in  this  appendix  will,  probably,  do 
more  harm  than  good. 

The  Same  Symbols  And  The  Same  Formulas  Are  Used  in 
these  solutions  as  those  which  are  employed  in  the  division 
which  precedes  the  problems  which  are  proposed  in  the  text 
portions  of  the  book. 

SOLUTIONS  TO  PROBLEMS  ON  DIVISION  1 
FUNCTION  AND  PRINCIPLE  OF  THE  STEAM  ENGINE 

1.  Head-end  displacement  volume  =  (10  X  10  X  0.785)  X  12  =  942 
cu.    in.      Crank-end    displacement  volume  =  942  -  [(1.5  X  1.5  X  0.785) 
X  12]   =  920.8    cu.    in.     Head-end    clearance    percentage  =  185  •*•  942 
=  0.196  or  19.6  per  cent.     Crank-end  clearance  percentage  =  180  -r-  920.8 
=  0.195  or  19.5  per  cent. 

2.  From  steam  tables,  the  total  heat  of  dry  saturated  steam  at  160  Ib. 
per  sq.  in.  abs.  =  1194.5  B.t.u.  per  Ib.     Also,  the  total  heat  of  steam  of 
89  per  cent,  quality  at  17  Ib.  per  sq.  in.  abs.  =  187.5  +  (0.89  X  965.6) 
=  1046.9    B.t.u.    per   Ib.     By    For.    (1):  Theoretical   efficiency  =  (Heat 
abstracted}  -r-  (Heat     received}  =  [(Heat     received}  —  (Heat     rejected}]  -r- 
(Heat  received}  =  [1194.5  -  1046.9[  -f-  1194.5  =  12.3  per  cent. 

3.  Area  of  piston  =  9  X  9  X  0.785  =  63.6  sq.  in.     Effective  pressure 
=  125  -  4  =  121  Ib.   per  sq.  in.     Hence,  by  For.  (3) :  W  =  AipL/8Pm 
=  63.6  X  1  X  121  =  7696   ft.    Ib.    per    working    stroke.     By    For.    (5): 
Pap  =  PmLfSAipNa  /33,000  =  (121  X  1  X  63.6  X  200)  -r  33,000  =  46.6 
h.p.  for  each  end.     Total  horse  power  =  2  X  46.6  =  93.2  h.p. 

4.  By  For.  (6):  Pm  =  Q.9[K(Pg  +  14.7)  -  Pa}.     Now,  from  Table  20: 

488 


SOLUTIONS  TO  PROBLEMS 


489 


K  =  0.737.  Also,  Pa  =  4  +  14.7  =  18.7  Ib.  per  sq.  in.  abs.  Hence, 
Pm  =  0.9[0.737(125  +  14.7)  -  18.7]  =  75.9  Ib.  per  sq.  in.  By  For.  (5): 
Pihp  =  PmL/^tpATs/33,000  =  (75.9  X  1  X  63.6  X  200)  -=-  33,000  = 
29.2  h.p.  for  each  end.  Total  horse  power  =  2  X  29.2  =  58.4  h.p. 

SOLUTIONS  TO  PROBLEMS  ON  DIVISION  3 
INDICATORS  AND  INDICATOR  PRACTICE 

1.  By  the  rules  of  Sec.  84,  length  of  diagram  =  4  X  12  -h  13  =  3.69  in. 
Radius  of  brumbo  pulley  =  13  X  3  -5-  12  =  3.25  in. 

2.  Length  of  diagram  =  (diam.  smaller  pulley  -v-  diam.  larger  pulley] 
X  stroke  =  (2  -f-  18)36  =  4  in. 

3.  By  method  of  ordinates,  mean  height  crank-end  diagram  =  1.048  in. 
mean  height,  head-end  diagram  =  1.006  in. 

4.  By  For.  (15)  mean  effective  pressure  =  Pm  =  mean  height  of  diagram 
X  scale  of  spring.     For  head-end  diagram:  Pm  =  1.006  X  60  =  60.36 
Ib.   per.   sq.  in.     For  crank-end  diagram:  Pm  =  1.048  X  60  =  62.88/6. 
per.  sq.  in. 

5.  By  For.  (13)  the  h.p.  constants  are:  For  head  end,  k\  = 


1.25   X    12   X    12   X   0.7854 


1.25    X    113.1 


33.000 

For    crank     end, 

1 
=  244'      By    F°r 


33,000 
1.25  X  (113.1  -  4.9) 


=    0.004284    = 


33,000 
1 
233' 


1.25  X  108.2 


33,000 

Pihp    =  PmNk. 


33,000 
For    head  end, 


X  220  X  233 


=  0.0041 

,  =  60.36 
1 


=  56.9  &.f>.     For  crank  end,   Pihp  =  62.88  X  220  X  ^h 
=  56.7  h.p.     Total  for  engine,  Pihp  =  56.9  +  56.7  =  113.6  h.p. 


Atmospheric  Line- 


Zero  Pressure  Line--—'' 
FIG.  547. — Solution  to  Prob.  6. 

6.  See  Fig.  547  which  shows  the  theoretical  expansion  and  compression 
lines. 

7.  Expansion  and  compression  curves  show  that  piston  and  exhaust 
valves  are  probably  in  good  order  but  that  there  is  steam  leaking  into  the 
crank  end  during  expansion.     Admission  is  early  at  the  head  end.     The 
steam  lines  show  a  marked  slope  probably  because  the  engine  is  under 
heavy  load. 


490  APPENDIX 

8.  By  For.  (21)  the  steam  rate  is 

1O    VKf) 

Wu  =     p      ((x8  +  xc)D'ps  -(x's  +  xc)D"ps]  Ib.  per.  i.h.p.  hr. 

m 

The  length  of  the  diagrams  in  Fig.  116  is  3^  in.  Values  of  xg  and 
x's  are  found  by  dividing  the  distance  of  a  point  from  the  end  of  the 
diagram  by  3^  in.  xc  is  given  in  Prob.  6  as  0.15.  Pressures  at  points 
are  taken  from  the  diagrams.  Densities  are  from  the  steam  table. 
Values  of  Pm  were  found  in  Prob.  4.  Values  of  the  several  terms  in  the 
formula  are  arranged  tabularly  below. 


Point 

R             S             X             Y 

Distance  from  end  of  diagram  (in.)  . 
Xq  or  x'a 

3.00         2.80         0.75         0.83 
0  923       0  862       0  231       0  256 

Pressure  (Ib.  per  sq.  in.  abs.) 

50             55             21             22 

Densitv  (Ib.  ver  cu.  ft.).. 

0.1175     0.1285     0.0521     0.054 

Substituting  in  For.  (21),  for  head  end: 

10  yen 

Wih  =-  [(0.862  +  0.15)0.1285   -(0.256   +  0.15)0.0545]     =     228 


[1.012  X  0.1285  -  0.406  X  0.0545]  = 

228(0.1301  -  0.0221)  =  228  X  0.108  =  24.6  Ib.  per  i.h.p.  hr. 
For  crank  end  : 

O-923  +  0.15)0.1175  -  (0.231   +  0.15)0.0521]    =   218.7 

[1.073  X  0.1175  -  0.381  X  0.0521]  = 
218.7(0.1261  -  0.0198)  =  218.7  X  0.1063  =  23.25  Ib.  per  i.h.p.  hr  . 

9.  By  the  rule  of  Sec.  131  and  from  the  results  of  Probs.  5  and  8,  total 
steam  used  per  hour  =  (56.9  X  24.6)  +  (56.7  X  23.25)  =  1399  +  1318  = 
2717  Ib.  per  hr. 

10.  By  planimeter,  area  of  head-end  diagram  =  3.23  sq.  in.;  area  of 
crank-end    diagram  =  3.38    sq.    in.     By    For.  (14),    head-end    Pm  = 

3.23  X  60  3.38  X  60 

—  5-^  —  =  59.6    Ib.    per  sq.  in.      Crank-end  Pm  =  —  5-^  —    =  62.4 

O.^O  O.AO 

Ib.  per  sq.  in. 


SOLUTIONS  TO  PROBLEMS  ON  DIVISION  6 

FLY-BALL   STEAM-ENGINE  GOVERNORS,  PRINCIPLES  AND 
ADJUSTMENT 

1.  By  -For.   (25),  the  coefficient  of  regulation  of  the  governor,  Mr  = 
Nn~  Nf  =  (201  -  197)  -5-  197  =  0.0203  =  2.0  per  cent. 


2.  By  For.  (27),  the  height,  Lhi  =  =  =  4.66  in. 


SOLUTIONS  TO  PROBLEMS  491 

3.  By    For.   '(26),    the  centrifugal  force,  Fc    =    0.000,028,5Wr,]V2  = 
0.000,028,5  X  6.25  X  4.32  X  5002  =  192.4  Ib. 

4.  The  governor  speed  remains  constant.     The  number  of  revolu- 
tions of  the  governor  per  engine  revolution  will  be  proportionally  less  to 
allow    the  additional  engine  speed.     That  is,  the  revolutions  will  be 

3-7  X  TT^  =3.1  revolutions  per  engine  revolution.     For  a  decrease  in  the 
iZo 

speed  ratio,  the  size  of  the  driving  pulley  must  be  proportionally  de- 
creased, that  is,  14  X ^25  =  UH  in.  =  the  required  diameter. 

W  _i_  w         Qf)  000 

5.  Substituting  in  For.  (28),  Lhi  =  — —^  X  -j^~,    there  results: 


16  =  --j£^-  X  ^P  from  which:  N*  =  28,800  and  AT  =  170  r.p.m. 

SOLUTIONS  TO  PROBLEMS  ON  DIVISION  8 
COMPOUND  AND  MULTI-EXPANSION  ENGINES 

1.  For  the  condensing  engine,  by  Sec.  287,  the  receiver  pressure  = 
supply     pressure  -*•  cylinder     ratio  =  (150  +  14.7) /4.3  =  38.3     Ib.  per 
sq.  in.  abs.,  or  38.3  —  14.7  =  23.6  Ib.  per  sq.  in.  'gage.     For  the  non-con- 
densing engine,  the  receiver  pressure  =  ^supply  pressure  X  back  pressure 

=    V(100  +  14.7)  X  (5  +  14.7)    =   47.5    Ib.    per   sq.    in.    abs.,  or  47.5 
—  14.7  =  32.8  Ib.  per  sq.  in.  gage. 

2.  Force    on    piston  =  (10  X  10  X  0.785)   X  150   =  11,780    Ib.     By 
Sec.  273:  Torque  =  0:90  X  11,780  X  6  =  63,600  Ib.  in. 

3.  Absolute  pressure  in  condenser  =  (30  —  28.5)  X  0.491  =  0.74  Ib. 
per  sq.  in.     From  steam  tables:  steam  temperature  at  0.74  Ib.  per  sq.  in: 
abs.  =  92  deg.  fahr.     Steam  temperature  at  (225  +  14.7)  =  239.7  Ib.  per 
sq.   in.   abs.  =  397   deg.  fahr.     Hence,   the   temperature  range  in  each 
cylinder  =  (397  -  92)  -=-  4  =  76.2  deg.' fahr. 

4.  Neglecting  clearance,  the  ratio  of  expansion  =  4.5  -f-  0.26  =  17.3. 
Considering    clearance    ratio    of    expansion    =  [4.5  +(0.06  X  4.5)]  -f- 
(0.26  +  0.06)  =  4.77  -^  0.32  =  14.9. 

6.  By  Sec.  291,  lead  =  5  X  KG  =  He  in. 

SOLUTIONS  TO  PROBLEMS  ON  DIVISION  10 

STEAM-ENGINE    EFFICIENCIES    AND    HOW   TO   INCREASE 

THEM 

1.  By  For.  (29),  the  efficiency  of  the  ideal  Rankine  cycle, 
„     _  tin  —  Htz 

The  total  heats,  Hti  and  Ht2,  are,  by  a  temperature-entropy  chart,  1190 


492  APPENDIX 

and  1003  B.t.u.  per  Ib.     The  heat  of  liquid,  Ht2  =  180  B.t.u.  per  Ib. 

Hence, 

„          1190  -  1003       .  10_ 

Edt  =   1190  -  180    =  °'185  =  18'5  per  CmL 

2.  By  For.  (30),  the  Rankine  cycle  water  rate, 

Wg  =      2545 

Hti  —  Htz 

The  steam  pressure  of  150  Ib.  per  sq.  in.  gage  corresponds  to  366  deg. 
fahr.  for  saturated  steam.  The  steam,  therefore,  has  550  —  366  =  184 
deg.  fahr.  superheat.  By  the  temperature-entropy  chart,  Hti  and  Ht% 
=  1295  and  955.  Hence, 

W'  =  1295^955  -"Oft-pr*.?.*. 

3.  By  For.  (31),  the  thermal  efficiency, 

2545 


W.i(Htl  -  Hi,) 
By  For.  (32),  the  total  heat  at  admission, 

Hn  =  xdHv  +  Hi  =  0.98  X  853  +  343  =  1179  B.t.u.  per  Ib. 
The  heat  of  liquid  at  exhaust,  Hu  (from  a  steam  table)  =  180  B.t.u.  per 
Ib.     Hence, 

'  °'138  ' 


-  180) 

4.  The  actual  thermal  efficiency  of  the  engine  in  Prob.  1,  by  For.  (31)  = 

2545  2545 

Edti  =  W«(Hn  -  Hn)  =  25(1190  -  180)  =  °-101  =  1(U  ^  ™*' 
By  For.  (34),  the  Rankine  cycle  ratio  = 

Actual  thermal  efficiency  _10.1  _nrt- 

Efficiency  of  the  ideal  Rankine  cycle      18.5 

5.  By  For.  (35),  the  mechanical  efficiency, 

Edm  =  ^  =.-J||  =  88.4  per  cent. 

JTihp  1»O 

6.  By  For.  (36)  the  over-all  efficiency, 

2545 


By  For.  (33),  the  total  heat  of  the  steam  admitted, 

Htl  =  Hd  +  TnCm  =  1196  +  100  X  0.58  =  1254  B.t.u.  per  Ib. 
The  absolute  back  pressure  =  29.8  —  27  =  2.8  in.  of  mercury  or  2.8 
-i-  2.03  =  1.4  per  sq.  in.  abs.     The  heat  of  liquid  at  this  back  pres- 
sure, HIZ  =  81  B.t.u.  per  Ib.     Hence  the  over-all  efficiency, 

E«  =  17.4(1%?-  81)  '  °'125  -  12'5  Per  Cent' 

7.  By  For.  (38),  the  British  thermal  units  per  brake  horse  power  hour  = 
Wsb(Htl  -  Hn)  =  17.4(1254  -  81)  =  20,400  B.t.u.  per  b.h.p.  hr.  or 
20,400  ^-  0.746  =  27,300  B.t.u.  per  kw.  hr. 


SOLUTIONS  TO  PROBLEMS  493 


8.  By  For.  (31),  the  thermal  efficiency, 
2545  2545 


19(1190  - 
for  the  first  engine. 


13-25  per  cenL 


for  the  second  engine.     The  engine  using  18  lb.  of  steam  per  indicated 
horse  power  hour  is,  in  this  case,  the  more  efficient. 

SOLUTIONS  TO  PROBLEMS  ON  DIVISION  12 
STEAM-ENGINE  TESTING 

1.  By  the  rule  of  Sec.  368,  the  mechanical  efficiency  =  brake  horse  power 
+  indicated    horse   power  =  120/133  =  0.903.     Friction   horse    power  = 
indicated  horse  power  —  brake  horse  power  =  133  —  120  =  13  h.p. 

f\     j      AT /'TXT'    TXT"    ~\ 

2.  By   For.    (41),    the  brake  horse  power  =  PbhP=  — ""  f  03  QQQ — 

2  X  3.14  X  5.25  X  220  X  (250) 

33,000   '  '  6Ap' 

3.  By  For.  (61),  the  brake  constant  =  kb  =0Jrn<{n=  — OQ  nnn  ' 

OO.UUvJ  OO.vJUU 

=  0.000,577. 

4.  By  For.  (54),  the  pounds  of  dry  steam  supplied  per  hour  =  W*d 
=  zdWsw  =  0.97  X  5000  =  4850  lb.     From   For.    (55),   the   water  rate 


i  =  24'25  lb'  dry  steam  per  l'h'p'  per  hr' 

5.  From  the  example  under  Sec.  373,  it  was  found  that  2499  lb.  of 

dry  steam  were  used  per  hour.     By  For.  (51),  the  horse  power  input  to 

the  generator   (brake  horse  power  when  belt  slip  is  neglected)  =  PhP 

Pkw          20.2  +  30.7 


0.746Ed      0.746  X  0.90 
W,d  2499 


75.8  h.p.     By  For.  (56),  the  water  rate  = 
=  33.0  lb.  of  dry  steam  per  b.h.p.  per  hr. 

'bhp    A   l-h          10'V    A    1 

Since  there  are  2550/75.8  or  33.6  lb.  of  wet  steam  used  per  brake  horse 
power  per  hour  the  thermal  efficiency  is,  by  For.  (36)  Div.  10, 

2545 2545 = 

dtb  ~  Wswb[(xdHv  +  Hi}  -  Hu      33.6[(0.98  X  856.8  +  338)  -  192.6] 

=  0.0769  =  7.7  per  cent,  thermal  efficiency  based  on  brake 


33.6(985.4) 
horse  power. 

6.  From  Sec.  368,  the  brake  horse  power  =  0.90  X  200  =  180  b.h.p. 


494  APPENDIX 

The  weight  of  wet  steam  used  per  hour  per  brake  horse  power  =  42,000/10 
X  180  =  23.3  Ib.     By  For.  (36),  the  thermal  efficiency  = 
p  2545 

= 


.  +  Hi)  -  H12]  ~ 
2545  2545 

23.3[(0.99  X  838  +  361.2)  -  203]  =  23^87^2)   =  °'1106  =  1L1    per 

cent,  thermal  efficiency  based  on  brake  horse  power. 


SOLUTIONS  TO  PROBLEMS  ON  DIVISION  16 
SELECTING  AN  ENGINE 

1.  The  energy  units  developed  per  year  =  10  X  300  X  250  =  750,000 
h.p.  hr.     By  For.  (63) :  Cost  per  unit  of  energy  =  Total  expenses  per  year 
-5-  Energy    units    developed   per   year  =  $15,000  -j-  750,000  =  $0.02  per 
h.p.  hr.  or  2  ct.  per  h.p.  hr. 

2.  By  Sec.  443,  depreciation  charge  =  $5000  -s-  28  =  $178.60, 

3.  DAILY  QUANTITIES: 


HOURS 

H.P.  HR. 

LB.  STEAM, 

LB.  STEAM, 

LOAD 

SERVICE 

CORLISS 

UNIFLOW 

IK 

3 

3,750 

93,400 

78,700 

Rated 

1 

1,000 

23,900 

20,100 

H 

53^ 

4,125 

95,000 

80,900 

H 

3% 

1,750 

41,850 

34,300 

H 

12 

3,000 

87,000 

60,900 

Totals  24  13,625  341,150  274,900 

Cost  of  steam  @  50  ct.  per  1000  Ib $170.58        $137.45 

Other  operating  costs  at  $1.50  per  hr 36.00  36.00 


Total  daily  operating  costs $206 . 58         $173 . 45 

YEARLY  QUANTITIES: 
Energy  units  delivered  =  300  X  13,625  =  '4,087,500  h.p.  hr. 

J300  X  206.58..                           ..$61,974 
Operating  charges,  { ^  x  m^ $52jQ35 

Fixed  charges  at  15  per  cent 1,500  1,950 

Total  annual  costs $63,474         $53,985 

AQ  A*7 A. 

Unit  energy  costs  (per  h.p.  hr.)  =  4  Qgy  500 SO  -0155 

'53,985 
"4,087,500 


SOLUTIONS  OF  PROBLEMS  495 
3.  From  Prob.  3: 

CORLISS  UNIFLOW 

Daily  operating  costs $    206 . 58  $  173 . 45 

Operating  costs  for  15  days 3,098 . 70  2,601 . 75 

Annual  Fixed  charges 1,500.00  1,950.00 


Total  annual  costs $4,598.70      $4,551 . 75 

Therefore,  uniflow  engine  would  have  smaller  annual  cost. 

Energy  output  in  15  days  =  15  X*13,625  =  204,375  h.p.  hr.     Cost  per 
unit  of  energy  =  $4,551.75  -5-  204,375  =  $0.0223  per  h.p.  hr. 


INDEX 


PAGE 


Absorption  dynamometers,  classifica- 
tion   347 

ACCEPTANCE  TEST,  definition 365 

how  conducted .  .    443 

Adiabatic  expansion 16 

Admission  line,  variations,  illustra- 
tion   61 

Advance  angle 99 

Air  leaks,  .source  of  trouble  in  con- 
densing operation 382 

Alignment,   engine,    method   used  in 

erection  and  re-assembling .  .   407 
Allis-Chalmers     heavy-duty     Corliss 
engine,  valve  gear,  illustra- 
tion     158 

American-Ball  engine  governor,  illus- 
tration    250 

American  Injector  Company,  crank- 
pin  oiler,  illustration 463 

AMERICAN  SOCIETY  MECHANICAL 
ENGINEERS,  "Test  Code," 
dry  steam  basis  for  com- 
puting engine  efficiency  304 

"Test  Code"  outline 369-371 

water-rate  test  specifications ....    365 
American    Steam    Gage    and    Valve 
Company,   Thompson  indi- 
cator, illustration 40 

AMES    "controlled-compression    una- 

flow"  engine,  illustration.  .  .  162 
engine,     Robb-Armstrpng-Sweet 

governor,  illustration 249 

four-valve  non-releasing  Corliss 
engine,  valve  gear,  illustra- 
tion   150 

"UNA-PLOW"  ENGINE  directions 
for  setting  poppet  valves 

182-186 

effect    of    valve    gear    adjust- 
ments, table 187 

AMES  IRON  WORKS,  directions  for 
setting  poppet  valves  on 
Ames  "una-flow"  engine 

182-186 
portable  boiler  and  engine  unit, 

illustration 322 

valve  gear   of   Ames   four-valve 

engine,  illustration 150 

Ammeter,  use  in  determining  output 

of  generator 354 

Amsler  polar  planimeter,  illustration.     73 
ANGLE-compound  engine,  definition  .  .      25 

of  advance,  definition 99 

ANGULARITY,  connecting  rod,  defini- 
tion and  effects 101 

eccentric  rod,  definition 102 

Ashcroft  Manufacturing  Company, 
Coffin  planimeter,  illustra- 
tion    75 

Atmospheric  line,  indicator  card,  how 

drawn 58 

AUTOMATIC  cut-off  governor 228 

ENGINE,  definition 228 

reversing  inadvisable '  •   235 

lubrication  systems  for  external 

bearings,  merits 470 


PAGE 

Automatic  Furnace  Company,  Model 
Acme  engine  trunk  piston 

m  echanism 35 

Auxiliaries,  inspection 375 

Auxiliary  piping  and  equipment,  non- 
condensing  engine,  illustra- 
tion   .375 


Babbitting,  engine  bearings :.  .  .  396 

Babbitt    recess,    method    of    closing, 

gating  and  venting 398 

BACK-acting   crank-mechanism 34 

pressure,    purpose    of    reducing 

with  condenser 285 

BALANCED  multiported  valve 91 

SLIDE    VALVE,    advantages    and 

disadvantages 89 

definition 26 

repair 394 

Ball  Engine  Company,  tandem- 
compound  engine,  illustra- 
tion    24 

BALL      four-valve      Corliss      engine, 

valve-gear,  illustration 174 

governor,  height  when  revolving  .  205 
"Banjo"  crank-pin  oiler,  illustration.  471 
BEARINGS,    adjustment    to    compen- 
sate for  wear 400 

engine,    temperature    after    run- 
ning short  time 379 

EXTERNAL,  definition 460 

drop-feed  lubrication 461 

lubrication  by  hand 460 

freshly  re-babbitted,  peening.  .  .  .  397 

friction  in  engines 301 

heating,  causes 402 

high  pressure,  oil  required 455 

inaccessible,  feeler  for  detecting 

heat 380 

inspection 374 

INTERNAL,  definition 460 

oil  feeding  by  hand 480 

loose,  knocks  caused  by 410 

MAIN,  see  also  Main  bearing. 

illustration 302 

re-babbitting  boxes  of 396 

mechanical  conditions 455 

method   of  scraping   high  spots, 

illustration 400 

oil,  table  of  uses  and  viscosities. .  .  459 

re-babbitting 395 

ring-oiled 464 

scraping 399 

SPLIT,  illustration 374 

adjustment 401 

surfaces,   reason  for  use  of  oils 

between 449 

wrist-pin  or  crank-pin,  heating .  .  403 
Bentley,    F.    W.    Jr.,    sight   feed   for 

drop-feed  oiler,  illustration.  464 
BOILER    feed-water,    equipment    for 

weighing 361 

foaming,     danger     with    super- 
heater    425 

PRESSURE,    increased,    effect    on 

engine  efficiency,  graph 294 


497 


498 


INDEX 


PAGE 
BOILER   PRESSURE  new  plant,   how 

selected 436 

stationary  power  plants,  prac- 
tical limits 295 

BOTTLE  OILER. 463 

illustration 465 

Bowser  oil  filtering  outfit,  operation .  .   477 
Bowser,  S.  F.,  and  Company,  Incor- 
porated,   filtering    and   cir- 
culation oil  system,  illustra- 
tion  • 468 

Bradley,  Alexander,  on  savings 
effected  by  superheating 

supply  steam,  table 423 

BRAKE  ARM,  effective  length,  defini- 
tion    349 

rope  brake,  illustration 351 

BRAKE  constant,  formula  for  calcula- 
ting   •. 368 

HORSE  POWER  calculation  when 
using  absorption  dynamo- 
meter, formula 349 

absorption  by  water  brake ....   352 
computation    from    indicator 

diagrams,  formula 78 

definition 78 

thermal    efficiency    based    on 

formula 310 

net-weight 349 

tare- weight,  definition 348 

Brakes,  classification 347 

Bridge  and  Beach  Manufacturing 
Company,  engine,  indicator 

diagram 332 

Brown  and   Sharpe  Company,   steel 

scale  with  end  graduations ..    122 

Brumbo  pulley,  definition 46 

Buckeye  Engine  Company,    "Buck- 
eye-mobile,"   illustration  . .  .   334 
BUCKEYE  ENGINE,  effect  of  superheat 

graph 423 

governor 251 

piston-type   riding-cut-off 

valve 135 

"BUCKEYE-MOBILE"  engine  unit,  il- 
lustration    334 

performance  graphs 335 

type  of  power  plant 333 

By-pass  automatic  valves,  on  condens- 
ing engines 184 

C 

Calculations,  indicator,  see  Indicator. 
Cam,  oscillating,  poppet  valve  motion 

given  by 161 

Center-crank  engine,  definition 20 

CENTRIFUGAL  FORCE,  definition 194 

developed  in  revolving  gover- 
nor weight,  formula ....  205 

governor 204 

permanent      control     in     shaft 

governors  effected  by 230 

shaft  governor  operation 229 

Centripetal  force,  definition 195 

Circulation  oils,  table  of  properties . .  .   456 
CHANDLER  AND   TAYLOR   COMPANY, 

piston  valve,  illustration ....  27 
splash-oiled  engine,  illustration . .  466 
engine,  Armstrong  governor, 

illustration 249 

variable  speed  engines,  trigger 
device  for  secondary  speed 

control 200 

Chill  point  of  oil 455 

CHUSE  ENGINE  AND  MANUFACTURING 
COMPANY,  condensing  uni- 
flow  engine,  valve  setting. . .  188 


PAGE 
CHUSE  ENGINE  AND  MANUFACTURING 

COMPANY,     Corliss  -valve 

mechanism    positively  oper- 

ated, illustration  ..........     29 

engine  indicator  diagram  ........ 

329,  331,  332 
governor,  illustration  ........... 

uniflow  engine,  illustration  ...... 

VALVE  setting  in  condensing  uni- 

flow engines  .............. 

stem  adjustment,  illustration. 
CLEARANCE,  inside,  slide  valve,  defi- 

nition .................... 

definition  ..................... 

proper  amount  between  journal 

and  bearing  ...............    402 

typical  values  in  different  type 

engines,  table  .............    297 

VOLUME,  definition  ......  :..-....        2 

determined  in  engine  testing  .  . 
effect  on  engine  efficiency  ..... 

Cleveland  open-cup  tester  for  flash- 

and  fire-point  tests,  illustra- 

tion ...................... 

Coffin  planimeter,  illustration  ....... 

Collins,  Hubert  E.,    "Shaft  Govern- 

ors,"    on     shaft     governor 

operation  ................. 

COMPOUND  ENGINE  ............   258-282 

advantages     and     disadvan- 

tages  ....................    260 

application  ...................    258 

classification  according  to  method 

of  transfer  of  steam  ........ 

condensing  operation  ........... 

correct  receiver  pressure   neces- 

sary for  economical  opera- 

tion ...................... 

definition  ..................  ... 

excessive  cylinder  condensation 

avoided  by  ............... 

how  governed  .................    225 

indicated    horse   power    compu- 

tation .............  .  .  .....   275 

marine,  forced-feed    lubrication, 

illustration...  ............    470 

mechanical      efficiency      greater 

than  that  of  simple  engine  .  .   264 
most     profitable     degree     of 

vacuum  ..................    289 

operation    through     large    tem- 

perature and  pressure  ranges  258 
receiver   pressure  dependent  on 

cylinder  ratio  ............ 

reduced    leakage   loss,    explana 

tion  ..................... 

saturation  line 

saving  greater  at  higher  boiler 

pressure  ................. 

single  valve,  uses  ............. 

,  • 

stopping  ..................... 

terms  used  in  connection  with. 
testing  .......................   366 

torque      or      turning     moment, 

evenness  increased  .........    265 

typical  piping,  illustration  ......    386 

use  of  superheated  steam  ....... 

valve  setting  .................. 

without     by-pass    valve,    start- 

ing ...................... 

COMPRESSION  curve,  effect  of  clear- 

ance volumes  on  ........... 

effect  of  different  exhaust  pres- 

sures on  ..................      69 

Condensation,  cylinder,  see  Cylinder 

condensation. 
CONDENSER,  barometric,  several  en- 

gines operated  with  ........    376 


239 
330 


188 
Ill 


95 
2 


366 
296 


454 
75 


239 


267 
387 


276 
23 


261 


278 


264 

272 


260 
323 


271 


424 
280 


387 
68 


INDEX 


499 


PAGE 

CONDENSER,  definition 283 

ejector-jet,  Corliss  engine,  illus- 
tration      284 


inspection. 


375 


low-level      jet,      connected      to 

engine,  illustration 286 

starting  and  stopping 381 

surface,  connection  to  tandem- 
compound  engine,  illustra- 
tion   284 

CONDENSING  ENGINE,  see  also  Engine, 
condensing. 

application 290 

definition 36 

CONDENSING  OPERATION 283-290 

adequate  water  supply  neces- 
sary    286 

advantages  and  disadvantages.  .    289 

change  to  non-condensing 382 

compound  engine 387 

definition 283 

importance  of  cylinder  con- 
densation in  determining 

economy 287 

methods    of    calculating     power 

increase  due  to 285 

non-condensing,         indicator 

cards 285 

trouble  caused  by  air  leaks 382 

when  not  economical 286 

CONNECTING     ROD,      angularity      or 

obliquity,  definition 101 

bearing,  illustration 302 

Constants,  engine  and  brake 368 

Cooper  Corliss  engine,  heat-insulated 

cylinder,  illustration 299  • 

Cord,  indicator,  method  of  arranging, 

illustration 59 

CORLISS  cross-compound  condensing 
engine,  manufacturer's  per- 
formance specifications 442 

detaching  valves,  dash  pots  for .  .    155 
ENGINE,  compound,  starting ....    386 
cut-off,    danger    of    lengthen- 
ing     172 

detaching,  stopping 385 

effects    of    valve-gear    adjust- 
ments, table 170-171 

ejector-jet  condenser,  illustra- 
tion      284 

four-valve  application 324 

governor,  starting  block 385 

hook-rod    or   reach-rod,    illus- 
tration      383 

ideal  steam  line  in 63 

indicator  card 70 

influence     of     superheat     on 

water-rate,  graph 423 

load  increased 173 

leads,     laps    and    trial    com- 
pressions table 169 

manufacturer's      performance 

specifications 441 

method  of  governing ^  .  .    195 

non-releasing,      starting      and 

stopping 380 

positively-operated,        advan- 
tages and  disadvantages ....    149 

running  over,  how  started 384 

SIMPLE  detaching,  starting.  .  .  383 
single-eccentric         detaching, 

valve-setting  directions  163-169 
starting  lever  and  wrist  plate, 

illustration 384 

valve  setting 163 

releasing  gear,  dash-pot,  troubles  412 
VALVE...  .    146-191 


PAGE 

CORLISS  VALVE,  advantages 146 

dash  pot,  illustration 159 

definition 28 

detaching     mechanism  or  trip 

gear,  typical  designs 155 

engine  efficiency  increased  by .    146 

GEAR,  illustration 151 

inverted  vacuum  dash-pot, 

illustration 412 

MECHANISM,    non-releasing    or 
positively    operated,   defini- 
tion ...... 30 

positively  operated,  descrip- 
tion      149 

moderate  superheat  advisable.    421 

reason     for     employing 146 

releasing  mechanism,  illustra- 
tion      152 

repair 395 

typical  designs 146 

TRIP  GEAR,  Vilter  engine,  illus- 
tration   ;..    156 

Nordberg       Manufacturing 

Company,  illustration ....   156 
COUNTERFLOW  ENGINE,  definition ....      32 
saturated     steam      operation, 

economies,  table 312-313 

using    superheated     steam,     oil 
supplied      by      atomization 

method 422 

CRANK-end   dead    center,    definition, 

illustration .  . .    103 

MECHANISM,    back-acting,    illus- 
tration        34 

standard,  definition 34 

PIN  BEARING,  heating 403 

wedge    and    shims  for  adjust- 
ment illustration 400 

PIN  OILER,  illustration 463 

truing  up  without  removing  .  .  .   402 
use  of  in  shaft  governor  in  place 

of  eccentric - .    239 

Crosby  outside-spring  indicator,  il- 
lustration   43 

CROSS-COMPOUND  Corliss  engine  gov- 
ernor, receiver-pressure  reg- 
ulation device,  illustration .  .  277 

ENGINE,  definition 24 

driving  alternator,  illustration  268 
CROSSHEAD  shoes,  method  of  adjust- 
ing, illustration 401 

velocity  variations  during  stroke  103 

Curved-slot  pencil  mechanism 43 

CUT-OFF,  apparent,  definition 16 

Corliss  engine,  danger  of  length- 
ening     172 

valve  operating-mechanism,  Mc- 
Intosh  and  Seymour  engine, 

illustration 94 

CYCLE,  engine,  definition 305 

ideal  Rankine 7 

CYLINDER  CONDENSATION,  causes  and 

prevention 297 

important  in  determining  econ- 
omy of  condensing  operation  287 
rejection     and     thermal     losses 

partly  caused  by 297 

CYLINDER     diagrams     superimposed 

upon  steam-chest  diagrams .      64 

EFFICIENCY,  definition 303,  309 

inspection 373 

OIL,  best  method  of  introducing.    478 
compounded  with  acidless  tal- 
low oil 458 

consumption  per  brake  horse- 
power, graph 432 

engines      using      superheated 
steam. . .  ....    421 


500 


INDEX 


PAGE 

CYLINDER  OIL,  grades,  table 458 

properties,  table 458 

ratio,   compound  engine,  defini- 
tion     271 

D 

D-SLIDE  VALVE,  definition 26 

disadvantages     partially     over- 
come       88 

repair 393 

DASH-POT,    Corliss    releasing    gears, 

troubles .....' 412 

definition  and  purpose 211 

detaching  Corliss  valves 155 

DEAD  CENTER,  definition,  illustration  103 
trammel      method     of      finding, 

illustration 104 

"Design  and  Construction  of  Heat 
Engines,"  W.  E.  Ninde,  on 

valve  diagrams 84 

Design-determined  equal  leads,  defi- 
nition   114 

DETACHING-CORLISS-VALVE  engine, 
advantages  and  disadvan- 
tages   153 

MECHANISM,  elements 153 

illustration 30,  152 

single-and  double-eccentric.    154 
Detroit  Lubricator  Company,   hand 

push  pump,  illustration 478 

DIAGRAM,  ideal  indicator,  illustration     60 
INDICATOR,  see  Indicator  diagram. 
leaky  exhaust  valve  revealed  by     66 

method  of  taking 58 

DIRECT  measurement,   valve  setting  108 

slide  valve 87 

DISPLACEMENT,  slide  valve,  definition  101 

'  "»     volume,      formula 3 

DouBLE-acting  engine,  definition ....      11 
beat  poppet  valve,  definition.  .  .  .    160 

ECCENTRIC    DETACHING    CORLIS8- 

VALVE  engine,  valve  setting.   172 

mechanism,  features 154 

engine,  definition 23 

flow  engine,  definition 32 

stroke,  definition 11 

Drains,  inspection 376 

DROP-cut-off  Corliss- valve  mechan- 
ism, illustration 152 

PEED      lubrication    of    external 

bearings 461 

oil  cup  with  sight  feed,  illus- 
tration      462 

oiler,    homemade    sight    feed, 

illustration 464 

Dummy      flywheel      method,      tare- 
weight  of  brake  found  by  ....  348 
Duplex-compound  engine,  definition.     24 
DYNAMOMETERS,  absorption,  classifi- 
cation   ' 347 

classification 346 

fluid-friction  type,  operation ....  352 
Prony  brake  type,  construction 

and  use 347 

rope  brake  absorption  type 350 

E 

ECCENTRIC  circle 98 

crank-end  extreme  position  illus- 
tration       120 

head-end  extreme  position,  illus- 
tration       120 

mechanism,  illustration 97 

motion  derived  from 98 

rod,  angularity,  definition 102 

setting  on  center 106 


PAGE 

ECCENTRICITY,  definition 98 

relation  to  valve  travel 99 

EFFICIENCY,   heat  of  liquid   basis  of 

calculation 306 

steam-engine,  how  increased  291-317 

theoretical,  formula 6 

ELECTRICAL  load,  measuring  in  poly- 
phase systems 356 

loading  of  engine 353-357 

output,  direct-current  generator, 

determination 354 

ENERGY  balance,  electric-energy  dis- 
tribution circuits,  illustra- 
tion    300 

cost,  factors 428 

electrical,  heat  unit  equivalent .  .        5 
mechanical,    heat    unit    equiva- 
lent          5 

ENGINE   alignment,    method ....   406-408 
angle-compound,  illustration.  ...      25 

annual  depreciation 431 

application  of  indicator 57 

automatic,  reversing  inadvisable  235 
bearings,  temperature  after  run- 
ning short  time 379 

center-crank,  definition 20 

cleaning 388 

clearance  values,  table 297 

COMPOUND,    see   also    Compound 
engine. 

and  multi-expansion 387 

four-valve,  steam  rates 329 

single-valve,  uses 323 

CONDENSING    and    non-condens- 
ing,     steam      consumption, 

table 286 

application 290 

definition 36 

operation,  definition 283 

constants,  calculation 368 

Corliss,  see  Corliss  engine. 

cost  per  unit  of  energy,  factors 

considered  in  computing ...    428 
counterflow  or  double-flow,  defi- 
nition   . 32 

cross-compound,  illustration ....     24 

CYCLE,  definition 305 

effects  of  slide  valve  adjust- 
ments, table 112 

data  form 413 

depreciation,  causes 430 

direction  of  rotation 22 

DOUBLE-acting,  definition 11 

definition 23 

duplex-compound,    illustration  .  .      24 
ECONOMY,  affected  by  clearance 

volume 296 

vs.  maintenance  charges 293 

with  saturated  steam,  table.  .  . 

316-317 

EFFICIENCY    BASED     ON     BRITISH 
THERMAL  UNITS  PER  kilowatt 

hour.- 304 

brake  horse  power  hour 304 

EFFICIENCY  BASED    ON   pounds   of 

coal  per  brake  horse  power 
hour 304 

pounds    of    coal   per   kilowatt 

hour 304 

EFFICIENCY   compared    to    ideal 

Rankine  cycle 309 

factors  determining 291 

heat  of  liquid  basis  of  calcula- 
tion     306 

increased      by      Corliss      and 
Poppet  valves 146 

mechanical 304 


INDEX 


501 


PAGE 
ENGINE  efficiency,  other  measures  of, 

formulas 310 

standards,  chart 303 

energy  cost  in  selecting 439 

EXPENSE,  insurance  cost.  . 429 

rent  charged  in  proportion  to 

floor  space 429 

taxes 430 

factors  determining  selection ....    434 
fitted  with  pantograph  and  indi- 
cators, illustration 47 

FIXED  charges 428 

cut-off,  definition 36 

four-valve     type,      construction 

and  use 324 

friction 301 

getting    out    of    line,    definition, 

causes 405 

gridiron-valve,  features 91 

heat  conversion  in 5 

HiGH-pressure,  definition 36 

SPEED,  definition 36 

indicator  diagram 62 

horizontal,  illustration 21 

in  line 406 

inclined,  illustration 21 

indicator  springs  selection 55 

indicators,  see  also  Indicators .... 

40-83 

inspection 373-377 

knocks,     causes    and    remedies, 

table 410 

laying  up 388 

left-hand,  illustration 21 

loading,  electrical 353-357 

long-stroke,  definition 32 

Low-pressure,  definition 36 

speed,  definition 36 

MECHANICAL  efficiency,  defini- 
tion, formula 310 

losses,  method  of  reducing ...     300 
mechanisms  and  nomenclature  19-38 

MEDiuM-pressure,  definition 36 

speed,  definition 36 

modern,  constructional,  opera- 
ting and  economic  charac- 
teristics   319-340 

MULTi-expansion,  see  also  Multi- 
expansion  engine. 

valve,  definition 32 

new,  valve  setting 112 

NON-CONDENSING,  definition 36 

SLIDE-VALVE,  starting 378 

stopping 380 

non-releasing    Corliss-valve, 

starting  and  stopping 380 

old,  valve  setting 113 

operating  costs 432 

OPERATION   conforming   to   load 

curve,  graph 438 

on  superheated  steam 422 

oscillating-cylinder,   illustration.      35 

out  of  line,  effect  on  bearings 405 

overhauling 388 

PERFORMANCE  and  maintenance, 

daily  record 414 

Rankine  cycle  used  as  stand- 
ard in  engine  testing 304 

records,  purpose  of  keeping. .  .  415 

plan   lay-out 406 

portable  slide-valve,  uses 323 

proper  management  purposes . .  .    373 
quadruple-expansion  vertical,  il- 
lustration        25 

RECIPROCATING,  see  also  Recipro- 

cating  engine. 

management,     operation    and 
repair 373-415 


PAGE 

ENGINE,  residual  or  scrap  value ....   431 
riding-cut-off  valve  type,  uses .  .  .   324 

right  hand,  illustration 21 

RUNNING  over,  definition 22 

UNDER,  definition 22 

knocks  in  guides 412 

saving  effected  by  superheating 

supply  steam,  table 423 

SELECTION 427-446 

chart. 440 

determination  of  speed  desired  435 
for  given  service,  procedure . . .  427 

for  new  plant 434 

governed  by  cost  per  unit  of 

energy  delivered 427 

operating    characteristics 

affecting 437 

proper  horse  power  determina- 
tion   435 

with    reference    to    operating 

conditions 436 

SHAFT-GOVERNED  piston-valve, 
setting  valve  for  design- 
determined  equal  leads, 

example 123-125 

valve  setting 114 

short-stroke  definition 32 

side-crank,  definition 20 

SIMPLE,  definition 22 

detaching  Corliss-valve,  start- 
ing    383 

four-valve,  steam  rates 328 

operation  profitable  at  low 
pressures  and  high  super- 
heats   425 

SLIDE-VALVE  automatic,   illus- 
tration     378 

illustration .' .  .        2 

siNGLE-acting,  definition 11 

-VALVE,  definition 32 

test  for  valve  leakage 389 

sizes,  selected  to  suit  load  curve .  438 
SLIDE-VALVE     condensing    start- 
ing      380 

direction  of  rotation  reversed .   140 
starting  and  stopping  unaffec- 
ted by  type  of  governor 378 

SPEED  for  direct-connected  gen- 
erator drive 436 

methods     of     adjustment     by 

governors,  illustrations 215 

splash-oiled,  illustration 465 

STEAM,  see  also  Steam  engine. 

function 1 

modern  types 319-340 

superheated  steam  used  in.   417-426 
taking    steam    for    full    stroke, 

illustration .-      10 

TANDEM-COMPOUND,  illustration.     24 

slide-valve,  starting 387 

TESTS,  data  and  results,  Ameri- 
can Society  of  Mechanical 

Engineers 369-371 

data  necessary,  table 343 

duration 365 

results  corrected  to  standard 

conditions 443 

TESTING 342-372 

clearance   volume  determined 

in 366 

equipment 344 

for  mechanical  efficiency 359 

procedure 343,  358 

thermal  efficiency  computation.   364 
throttling-governed  direct- valve , 
setting    valve    for    selected 

equal  leads  example 122 

total  annual  cost 427,  433 


502 


INDEX 


PAGE 
ENGINE,     total,     steam     used     per 

hour 81 

TRiPLE-compound,  definition.  ...      25 

expansion,  illustration 25 

twin-cylinder,  illustration 23 

types,  classification 19 

UNIFLOW,  construction  and  opera- 
tion    331 

definition 33 

poppet  valve,  starting 385 

UNIT     ENERGY     COST,      COMPUTA- 
TION, formula 427 

example 434 

unit,  typical,  illustration 322 

VALVES  for  use  with  highly  super- 
heated steam 419 

maximum  pressures  and  super- 
heats,   table 421 

methods   of   control   by   shaft 

governor 239 

VARiABLE-cut-off ,  definition 37 

speed,  definition 216 

vertical,  illustration 20 

warming   facilitated   by  by-pass 

to  both  ends  of  cylinder 379 

WATER  RATE   calculation,  based 
on    indicated    horse    power, 

formula 363 

determination  by  steam  con- 
denser     357 

weight  of  steam  used  computed 

from  indicator  diagram 80 

ERIE  BALL  ENGINE  COMPANY,  direc- 
tions for  setting  Ball  Corliss 

engine  valves 173 

piston  valve  engine,  illustration .  420 
simple   balanced-slide-valve    en- 

'   gine,  illustration 321 

Sweet  valve,  illustration 90 

ERIE  CITY  IRON  WORKS,  single-cylin- 
der Lentz  engine,  illustra- 
tion . 326 

valve  setting  directions  for  Lentz 

poppet-valve     engine..    188-190 
Erie  Engine  Works,  simple  slide-valve 
automatic    engine,    illustra- 
tion      378 

ERIE  governor,  Jarecki  Manufactur- 
ing Company,  table  of  sizes.  224 

pump  governor,  illustration 197 

EXHAUST  line,  purpose 67 

pressure,  effect  on  compression, 

graph 69 

EXPANSION    curve,    ideal    compound 

engine 272 

free,    compound    engine,    defini- 
tion      271 

larger     cylinder     necessary     for 

given  work  output 13 

LINE,  leaky  valves  revealed  by ...     66 

STEAM,  form  of  curve 16 

engine 65 

theoretical,  graph 66 

RATIO  OF,  definition 260 

work  to  heat  increased  by 13 

steam,  work  done 12 

total    ratio,    compound    engine, 

definition 271 

EXTERNAL  BEARING,  definition 460 

lubrication,  see  Lubrication,  exter- 
nal bearing. 

External  slide  valve 87 

"Extra  Hecla"   cylinder  oil  for  use 

with  superheated  steam ....  422 


Feed-water  and  steam  cycle  in  power 

plant,  illustration 306 


PAGE 

Feeler,  heating  of  inaccessible  bear- 
ings detected  by,  illustration  379 

Fessenden,  C.  H.,  "Valve  Gears" 84 

FILTER,  OIL,  illustration  from  "South- 
ern Engineer" 474 

improvised 476 

operation 474 

"Power,"  illustration 475 

precipitation        compartment, 

illustration 477 

Richardson-Phenix       Company, 

illustration 476 

Filtering  and  circulation  oil  system, 

illustration 468 

"Financial  Engineering,"  O.  B.  Gold- 
man, steam  consumption  of 
condensing  and  non-con- 
densing engines 286 

Fire-point  of  oil 454 

FITCHBURG  ENGINE,  direct  of  rotation 

changed 255 

valve  mechanism,  illustration.  .   325 
FITCHBURG  governor,  illustration  and 

operation 254 

Fixed-cut-off  engine,  definition 36 

Flash-point  of  an  oil,  definition 454 

FLEMING-HARRISBURG  engine  gov- 
ernor, adjustments 249 

four-valve  engine,   valve-setting 

directions 175-178 

FLY-BALL       GOVERNOR,       adjustable 

thrust  bearing,  illustration.  225 
adjustments    and    their    effects, 

table 221 

definition 38,  193 

methods  for  controlling  steam  . .  .    195 
neutral    or    isochronous,    defini- 
tion      204 

principles  and  adjustment .  .    192-227 
speed  variation  permitted  by ....    195 

stable  or  static,  definition 204 

unstable  or  astatic,  definition . .  .    204 

weight-  or  spring-loaded 207 

FLYWHEEL,  direction  of  rotation 22 

inspection 374 

method  of  balancing,  illustration  236 

shaft  governor,  balance 235 

Foaming  boiler  danger  with  super- 
heated steam 425 

FORCE-FEED  CIRCULATION  SYSTEM, 
advantages  and  disadvan- 
tages   471 

external-bearing  lubrication ....    469 

table  of  oils  used 459 

FORCE-FEED  lubricator,  see  also 
Lubricator,  force-feed. 

pump,  illustration 484 

Foster    superheater    catalogue    effect 

of  superheat,  graph 423 

FOUR-VALVE     ENGINE,     construction 

and  use 324 

low  steam  rate 327 

FOXBORO  MANUFACTURING  COM- 
PANY, continuous  revolution 

counter,  illustration 345 

hand  tachometer,  illustration .  .  .   346 

FRICTION,  definition 448 

fluid,  definition .  .  . 447 

horse  power,  definition 77,  342 

SLIDING,  definition 448 

when  replaced  by  fluid  friction  449 

rolling,  definition 447 

FULTON  IRON  WORKS  COMPANY, 
St.  Louis,  cross-compound 

engine,  illustration 268 

Corliss  engine,  illustration 165 

live-steam  reheater  and  receiver, 

illustration 269 


INDEX 


503 


PAGE 

FULTON      IRON     WORKS    COMPANY, 
receiver-pressure   regulation 

device,  illustration 277 

Fulton-Corliss  cross-compound  engine, 

assembly  drawing 329 


G 


211 


Gappot  definition  and  purpose 

Gardner   throttling  governor,   spring 

arrangement,  illustration .  . .    209 
"Gargoyle"  cylinder  oil  for  use  with 

superheated  steam 422 

Gear  adjustment  on  governors 278 

Gears,   Corliss  releasing,   troubles  of 

dash-pots 412 

GEBHARDT    "STEAM    POWER    PLANT 
ENGINEERING,"    frictional 

losses  of  engines 301 

steam    engine    efficiencies     and 

performance  tables.  .  .  .    311-317 
GENERATOR,  direct-current,  determi- 
nation of  electrical  output ..   354 

efficiency 355 

electric,  for  engine  loading 353 

horse  power  input  determination, 

formula 355 

loading  by  water  rheostat 357 

power  output,  formula 354 

Gland  friction  in  engines 301 

Goldman,  O.  B.       "Financial    Engi- 
neering,"  steam   consumption 
of     condensing     and     non- 
condensing  engines 286 

Governing      high-pressure      cylinder 
only,      effect     on     receiver 

pressure 279 

GOVERNOR,    see    also    Shaft   governor 

and  fly-ball  governor. 
ADJUSTMENT  for  different  speeds 
by     adding     or     removing 

weight 213 

for     promptness     and     speed 

regulation 219 

to  change  engine  speed 212 

American-Ball  engine 250 

attentions  required 225 

BELT,  requirements 201 

oily  or  slack,  danger 201 

Buckeye,  illustration 251 

centrifugal  force 204 

classification 193 

Corliss  engine,  illustration 192 

dash-pot  size  varying  with  load 

conditions 211 

definition 192 

effect  on  slide-valve  setting 140 

enclosed  spring,  illustration 202 

engine,  functions 37 

Erie  pump,  illustration 197 

failure,  engine  and  power  plant 

wrecks  due  to 198 

Fitchburg  type,  setting 254 

Fleming-Harrisburg     centrifugal 

inertia,  illustration 250 

FLY-BALL,      see      also      Fly-ball 

governor 192-227 

definition 193 

illustration 38 

principles  and  adjustment  192-227 
flywheel  in  balance,  explanation.  235 
forces  for  detecting  engine  speed 

variations 194 

GEAR  adjustment 278 

example  of  changing 217 

"Hamilton"      uniflow     poppet- 

valve  engine,  illustration  .  .  .   255 
horizontal  tension  spring,  illus- 
tration      194 


PAGE 
GOVERNOR, hunting, definition  of  term  210 

in  balance,  explanation 235 

incorrect     application     or     poor 

condition,  danger 222 

lagging  during  changes  in  load, 

causes 223 

LEVERS,  adjustable,  illustration . .  219 

method  of  securing 201 

load  indicator  for 223 

Mclntosh  and  Seymour,  illustra- 
tion    253 

MECHANISM,     binding,     dangers 

due  to 201 

construction 201 

performance,      terms     used     to 

describe 203 

Porter,  relation  between  speed, 
height  and  weights  of  balls 
and  counterpoise,  formula .  .  208 

position  for  starting  engine 385 

pulley,          requirements         and 

methods  of  securing 201 

Rites  type,  Troy  vertical  engine, 

illustration 247 

Robb-Armstrong-Sweet        type, 

illustration 248 

safety  and  reliability  devices ....   198 
sensitiveness       changing       with 

speed  changes 216 

SHAFT,  see  also  Shaft  governor. 
full-load  running  position,  how 

found 141 

principles  and  adjustments.  .  . 

228-257 
SIMPLE  PENDULUM,  angular  speed 

and  ball  height 205 

ball  height,  formula 206 

spring-  or  weight-loaded,  advan- 
tages over  simple  pendulum  207 

steam-engine,  classification 37 

THROTTLING,  selection 224 

table  of  sizes 224 

typical  shaft,  illustration 37 

unstable,  useless  for  engineering 

purposes 204 

vibration,  causes 223 

weight,     revolving,     centrifugal 

force  developed  formula ....   205 
wheel,    Troy   automatic    engine, 
method  of  balancing,  illus- 
tration      236 

when  necessary 193 

rod     pivots,     proper    end-play, 

illustration 202 

"Governors    and    the    Governing  of 
Prime  Movers,"  W.  Trinks, 

on  racing 222 

Graphite,    flake,    use    in    valve    and 

cylinder  lubrication 479 

GRAVITY-CIRCULATION    SYSTEM,    ad- 
vantages    470 

external-bearing   lubrication.  .  .  .  467 
GRAVITY  oiling  system,  four-window 

sight-feed  oiler,  illustration .  .  468 
TRIP  GEAR,    "Hamilton"  Corliss 

engine,  illustration 155 

Murray   Corliss  engine,  illus- 
tration     157 

valve,  MacCord  Manufacturing 

Company,  illustration 479 

GRIDIRON  VALVE,  definition 28 

engine,  features 91 

Grpssenbacher,  E.,  oil  filter,  illustra- 
tion    475 

H 
HAMILTON    Corliss    engine,    gravity 

trip  gear,  illustration 155 


504 


INDEX 


PAGE 

HAMILTON,  engine  cylinder,  detach- 
ing-poppet admission  valve, 

illustration 32 

UNIFLOW      ENGINE,      governing 

mechanism 255 

poppet-valve  engine  cylinder, 

illustration 420 

HAMKENS,  "STEAM  ENGINE  TROU- 
BLES," enclosed-spring  gov- 
ernor illustration 202 

governor    employing    horizontal 

tension  spring  illustration . .   194 

governors 193 

HARDING  AND  WILLARD,  "MECHANI- 
CAL EQUIPMENT  OF  BUILD- 
INGS," Corliss  engine  gov- 
ernor, illustration 192 

on  regulation  guarantee  tests ....   204 
"Hardwick"     shaft    governor,     Erie 

engine,  illustration 237 

Harrisburg  Foundry  and  Machine, 
Works,  "Fleming-Harris- 
burg"  engine  valve-set- 
ting..   175-178 

HARRISBURG  FOUR-VALVE  ENGINE, 
advance  of  steam  and  ex- 
haust valve  arms,  table.  .  .  .  178 

exterior  outline 176 

HEAD-END    dead    center,    definition, 

illustration 103 

port  opened  to  extent  of  lead, 

illustration 121 

HEAT,  abstracted 9 

as  energy 5 

BALANCE,  explanation 8 

high-grade  engine,  illustration       9 
plant  with  condensing  engine 

using  live  steam  for  heating  299 
power     plant     where     engine 

exhaust  is  used  for  heating.  .   298 
conversion  in  engine,  example  .  .        7 

converted  into  work 9 

energy,  conversion  into  mechan- 
ical work 1 

insulation    or    lagging,    thermal 

losses  reduced  by 299 

mechanical  losses 9 

rejected,  in  steam  engine 6 

thermal  losses 9 

total,  small  part  converted  into 
mechanical  work  by  steam 

engine 291 

transfer,    saturated    and  super- 
heated steam  plants,  diagram  417 
unit   equivalents   in   mechanical 

and  electrical  energy 5 

useful  work 9 

flow,  steam-engine  plant,  expla- 
nation          1 

insulated  engine  cylinder,  illus- 
tration     299 

HiGH-pressure  engine,  definition 36 

SPEED  ENGINE,  definition 36 

testing 366 

HlLLS-McCANNA       COMPANY,       fqrCC- 

feed  lubricator,  illustration.    484 

pump,  illustration 484 

Hirshfeld     and     Ulbricht,      "Steam 

Power,"  engine  classification     19 
Holstead    Mill    and    Elevator    Com- 

§any,       engine       indicator 
iagram 331 

Hook-rod,  Corliss  engine,  illustration  383 
HOOVEN,  OWENS,  RENTSCHLER  COM- 
PANY, Corliss-engine  valves, 

illustration 147 

poppet-valve     engine     cylinder, 

illustration 420 


PAGE 
Horizontal  steam  engine,  definition .  .     20 

HORSE  POWER,  brake,  definition 78 

computation       from      indicator 

diagrams 76 

constant,  formula 76 

definition 14 

each     end     of     cylinder,     how 

found 77 

FRICTION,  definition 77,  342 

variation    with    brake     horse 

power 301 

INDICATED,    compound    engines, 

computation 275 

definition 77 

formula  for  computing 76 

input  to  generator,  known  out- 
put, formula 355 

of   engine,    mean   effective   pres- 
sure necessary  to  determine.      70 
HUNTING,     governor,     definition     of 

term 210 

graphs  of  governors 210 

shaft  governor,  cause 243 

Hydrometer,   use   in   finding   specific 

gravity  of  oil 453 

HYDROSTATIC    LUBRICATOR,    see   also 
Lubricator,  hydrostatic. 

illustration 481 

Hyperbolic  expansion  line  for  steam, 

graph 65 


"IDEAL"      CORLISS-VALVE      ENGINE, 

Corliss  valve,  illustration.  147 

shaft  governor  illustration 249 

Ideal  Rankine  cycle  efficiency,  form- 
ula for  computing 305 

iNCLiNED-plane  reducing  mechanism .  49 

steam  engine,  definition 20 

INDICATED  HORSE  POWER,  definition.  77 
thermal  efficiency  computa- 
tions based  on  formula 307 

INDICATOR,  application  to  engine 57 

cards,      condensing      and      non- 
condensing  operation 285 

cock,  relief  passage 51 

connection  to  cylinder,  illustra- 
tion   51 

CORD,    connection  to   crosshead, 

illustration 48 

methods  of  hooking  up 58 

Crosby    outside-spring,    illustra- 
tion    43 

definition 40 

DIAGRAMS,  actual  and  theoretical  61 

areas  found  by  planimeter ....  73 
brake   horse  power   computed 

from,  formula 78 

combined,      quadruple-expan- 
sion engine 281 

compound      and      equivalent 

simple  engine 265 

engine  faults  revealed  by 69 

high-speed  engine 62 

horse  power  computed  from  ...  76 

ideal 60 

leaky    steam-admission    valve 

revealed  by 66 

MEAN,  method  of  drawing 275 

when  necessary 274 

method  of  taking 58 

steam  weight  computed  from .  80 

uses 40 

incorrect  piping,  illustration 52 

modern,  variation  from  Watt's .  .  42 
paper,   requirements   and  place- 
ment on  drum 57 

PENCIL  mechanism,  advantages.  42 


INDEX 


505 


PAGE 

INDICATOR  PENCIL,  method  of  adjust- 
in? • f.6, 

requirements -.      08 

piping  for 50 

practice 40-83 

REDUCING,      adjustable      panto- 
graph for,  illustration 47 

MECHANISM,  classification 44 

when  necessary 43 

motion,  tests  before  using ....      49 
single,    for     cylinder,    disadvan- 
tages       51 

SPRING,  adjustment 56 

card  illustrating  test 54 

classification 52 

for  engine,  selection 55 

periodic  tests  necessary 53 

safe  pressures,  table 53 

scale,  formula 54 

test 53 

two,  operated  from  one  reducing 

mechanism,  illustration ....  57 
use  in  valve-setting  operations.  .  142 
valve  setting  defects  determined 

by 143-144 

Watt's,  illustration 41 

INDIRECT    measurement    method    of 

ascertaining  valve  operation  108 

slide  valve 87 

INERTIA,    principle    of,     applied    to 

revolving  governing  parts.  .   231 

shaft  governor  operation 229 

temporary      control      in      shaft 

governor  effected  by 231 

Inside-admission  slide  valve 87 

Instruments,  inspection 376 

Insulation,    thermal    losses    reduced 

by 299 

Interheater,  definition 269 

INTERNAL  bearings,  definition 460 

lubrication,  see  also  Lubrication, 

internal 478-486 

slide  valve ...  ,87 


Jarecki  Manufacturing  Company, 
throttling  governor  sizes, 
table 224 

Jig,  for  boring  babbitted  bearing 

boxes 398 

Journal  and  bearing,  clearance 

between 402 


Kahl,  J.  C.  oil  filter,  illustration 474 

KNOCK,  apparent  location  deceptive.  410 

causes  and  remedies 410 

location  ascertained  by  sounding 

rod .  .   412 


LAP  angle,  definition,  illustration 100 

steam  and  exhaust,  purposes ....     95 

valve,  definition 94 

Lapping  plate 392 

LEAD  angle,  definition,  illustration . .  .   100 

explanation  of  term 96 

measurement,  illustration 124 

proper  for  slide  valve 115 

LEADS,    EQUAL,    designed-determined 

definition 114 

selected,  definition 114 

Leads,   laps  and  trial   compressions, 

Corliss- valve  engine,  table .  .    169 
Leakage     loss,     less     in     compound 
than      in      simple      engine, 

explanation 264 

Left-hand  engine,  definition ...  21 


PAGE 

LENTZ  ENGINE,  high-pressure  steam- 
valve  gear,  illustration 189 

poppet-valve,  valve  setting  direc- 
tions    188-190 

report  on  record  steam  rate  for 

uniflow  engine 332 

single-cylinder,  illustration 326 

LEVER,  governor,  method  of  securing.    201 
pencil     mechanism,     Thompson 

indicator,  illustration 44 

Life  of  engine,  effect  on  selection  of 

engine 437 

Lineal  clearance,  definition 3 

LOAD  curve,  power  plant,  for  engine 

selection 437 

ELECTRICAL,  determination  with 
three-phase  alternating-cur- 
rent generator 356 

of  engine 353-357 

factor  of  power  plant,  definition.    438 
indicator   for   engine   governors, 

illustration 223 

-measuring  apparatus,  classifica- 
tion    346 

-output  determination,  direct- 
current  generator,  illustra- 
tion    354 

Locomobile  steam  engine  unit 333 

Long-stroke  engine,  definition 32 

Losses,  steam-engine,  classification .  . .    293 

Loss,  mechanical 8 

Low-pressure  engine,  definition 36 

-speed  engine,  definition 36 

LUBRICANTS,  classification 450 

semi-solid,  uses 451 

solid,  use 450 

LUBRICATION,  automatic,  for  external 

bearings,  merits 470 

chart,      steam      cylinders      and 

valves 457 

DROP-PEED,  applications  suitable 

for  steam  engines 462 

of  external  bearings 461 

engine 447-487 

EXTERNAL  BEARINGS,  by  hand .  .  .  460 
force-feed  circulation  system .  .  469 
gravity-circulation  system ....  467 

splash  system 465 

force-feed,      compound      marine 

engine  with,  illustration. .  .  .  470 

iNTERNAL-bearing 478-486 

of     engines,     automizer     for, 

illustration 479 

purpose 447 

stuffing  boxes 480 

SYSTEM,  choice  of  oil  affected  by .  456 
for  external  bearings,  classifi- 
cation      460 

steam  engines,  classification .  .  .  460 
"Lubrication,    Practice    of,"    T.    C. 
Thomson,    selection    of    oils 
for  engine  lubrication,  tables 

456-460 
LUBRICATOR,  FORCE-FEED,  illustration  484 

installation 485 

LUBRICATOR,  HYDROSTATIC,  care  and 

operation 482 

leakages  of  joints  or  packing ....  483 

prevention  of  trouble 483 

principle 480 

water  feed  valve 483 

LUBRICATOR,  independent  or  central, 

starting 378 

mechanical  force-feed 483 

Meyeringh  proportional,  illus- 
tration    486 

multiple-feed  mechanical 485 

proportional,  definition 485 


506 


INDEX 


PAGE 
LUNKENHEIMER  COMPANY,   auxiliary 

graphite  feeder,  illustration .   480 
drop-feed  oil  cup,  illustration ....    462 
Lever-handle  oil  pump,  illustra- 
tion     480 

Me 

MdNTOSH    AND    SEYMOUR    four-Valve 

engine 324 

governor 253 

gridiron  valve,  illustration 28 

engine,  valve  construction 93 

valve-operating       mechanism, 

illustration 92 

M 

MacCord   Manufacturing  Company, 

gravity  valve,  illustration..   479 

MAIN  BEARING  box,  pouring 397 

boxes,  babbitted  while  warm.  .    397 

correct  oil  grooves 399 

heating 403 

method  of  gaging  wear 410 

normal  wear,  effect  on  shaft 409 

quartered,    dismantling    for    re- 
babbitting 396 

Main-valve  operating  mechanism, 
Mclntosh  and  Seymour 

engine,  illustration 93 

Mandrel,    use    in    babbitting    main 

bearings 397 

Marker,  stationary,  method  of  plac- 
ing engine  on  dead  center .  .    105 
MARKS    "MECHANICAL    ENGINEERS' 
HANDBOOK,"  clearance 

values,  table 297 

Rankine  cycle  rates,  table 309 

Marine  engine,  four-cylinder  triple- 
expansion,  illustration 280 

MEAN  EFFECTIVE  PRESSURE 12 

formula  for  computing 15 

Mean  indicator  diagram,  when  neces- 
sary    274 

Measuring  rod,  head 126 

MECHANICAL  EFFICIENCY  of  engine, 

definition,  formula 310 

TEST      apparatus,      for      simple 

engine 360 

data  sheet 360 

purpose 342 

"MECHANICAL  ENGINEERS'  HAND- 
BOOK," clearance  values, 

table 297 

Rankine  cycle  rates,  table 309 

"MECHANICAL  EQUIPMENT  OF  BUILD- 
INGS," HARDING  AND  WIL- 
LARD,  Corliss  engine  gover- 
nor, illustration 192 

regulation  guarantee  tests 204 

MECHANICAL  LOSSES,  definition. .  .   8,  294 

methods  of  reducing 300 

Mechanical  work,  small  part  of  total 
heat  converted  into  by 

engine. 291 

Mechanisms,  engine 19-38 

MEDiuM-pressure  engine,  definition.  .      36 

-speed  engine,  definition 36 

Meyeringh    proportional    lubricator, 

illustration 486 

Meyer  riding-cut-off  valve,  illustra- 
tion   28,  134 

Model    Acme    engine,    trunk    piston 

mechanism,   illustration....     35 
Monel  metal,  for  valves   used   with 

superheated  steam 421 


PAGE 

MULTI-EXPANSION     ENGINE  258-282 

advantages  and  disadvantages.  .    260 

application 258 

best      receiver      pressure,      how 

found 276 

saturated  steam  operation  econo- 
mics, table 314-315 

stopping 387 

MULTIPORTED  slide  valve,  advan- 
tages and  disadvantages.  ...  90 

VALVE,  definition 27 

setting 131 

Multi- valve  engine,  definition 32 

MURRAY  IRON  WORKS,  Burlington 
Iowa,  Corliss-valve  dash 

pot,  illustration 159 

governor    adjusted    by    weight, 

illustration 213 

gravity  trip  gear  illustration 157 

N 

"National  Engineer,"  T.  G.  Thurs- 
ton,  gravity-circulation  sys- 
tem, illustration 469 

Newton,      Sir     Isaac,     principle     of 

inertia 231 

Ninde,  W.  E.,  "  Design  and  Construc- 
tion of  Heat  Engines,"  on 
valve  diagrams 84 

NON-CONDENSING    ENGINE,    see    also 

Engine,  non-condensing. 
auxiliary      piping     and      equip- 
ment, illustration 375 

definition 36 

Non-condensing  operation 283-290 

Non-releasing    Corliss-valve    engine, 

starting  and  stopping 380 

NORDBERG  engine,  positively-oper- 
ated poppet  admission 

valve,  illustration 31 

engine,   variation  in  steam  con- 
sumption    294 

governor,  spring-connected  dash- 
pot  rod 212 

long-range  valve  gear  and  gov- 
ernor     156 

standard     Corliss     valve     gear, 

illustration 159 

Nordberg  Manufacturing  Company, 

Corliss  trip  gear,  illustration  156 

Nugent  crank-pin  oiler,  illustration.  .   471 


Obliquity,  connecting  rod,  definition 

and  effects 101 

OIL  barrels,  methods  of  handling 452 

chill  point,  definition 455 

choice  affected  by  type  of  lubri- 
cating system 456 

circulation,  table  of  properties. .  .    456 

classification 451 

collecting  devices,  illustration. .  .   472 

compounded,  definition 451 

CYLINDER,    engines   using  super- 
heated steam 421 

table  of  grades 458 

table  of  properties 458 

deposit-forming 456 

filtering  outfit,  S.  F.  Bowser  and 

Company,  Incorporated.  . .  .   478 
FILTER,  see  also  Filter,  oil. 

filtering  materials  used 474 

fire-point,  definition 454 

fixed,  definition 451 

flash-point,  definition 454 


INDEX 


507 


PAGE 
OIL,   force-feed  circulation    systems, 

table 459 

groove,  cutting,  illustration 400 
igh-speed  splash-oiled  engines, 

table 460 

methods  of  supplying  to  moving 

bearings 471 

mineral,  definition 451 

PURIFIER,  operation 474 

capacities 476 

selection,  requirements  to  be  met  455 

specific  gravity,  how  found 453 

steam-engine  lubrication,  selec- 
tion, tables 456 

swing  joints  for  supplying  crank 
and  crosshead  pins,  illustra- 
tion   473 

system,  filtering  and  circulation 

type,  illustration 468 

tests  for  properties 452 

viscosity,  measurement 453 

Oil  Well  Supply  Company,  Pitts- 
burgh, Meyeringn  propor- 
tional lubricator,  illustra- 
tion   486 

OILER,  bottle  type 463 

crank-pin,  illustration 463 

crosshead-pin  telescopic,  illus- 
tration   472 

drop-feed 461 

Oiling,  hand 461 

Operating-condition  test,  purpose ....    342 
Ordinates,    method    of,    for    finding 

mean  effective  pressure,  graph  ...      71 
Oscillating-cylinder  engine,  definition     35 
Output,  electrical,  direct-current  gen- 
erator,      354 

Outside-admission  slide  valve 87 

Over-all    efficiency    based    on    brake 

horse  power,  formula 310 


PACKING,   metallic,   used  with  high- 
pressure  superheated  steam .   422 

rings 392 

sheet,  for  valve-chest  covers  and 

flanged  joints 404 

soft,  replacement 405 

steam  engine 403 

stuffing  box,  correct  and  incor- 
rect arrangement,  illustra- 
tion   405 

PANTOGRAPH  as  an  indicator  reducing 

mechanism 46 

engine  fitted  with,  illustration.  .  .     47 
Paper,    indicator,    requirements    and 

placement  on  drum 57 

Parallel-link  pencil  mechanism 43 

PEENING  in  main  bearing-box 398 

snap  packing  ring 393 

PENCIL,  indicator,  requirements 58 

MECHANISM,  indicator,  advan- 
tages   42 

types 43 

PENDULUM,  angular  speed  and    ball 

height 205 

LEVER,  inverted,   with    Brumbo 

pulley,  illustration 45 

reducing  mechanism,  construc- 
tion    44-46 

SIMPLE,  ball  height,  formula 206 

or   Watt's   governor,    illustra- 
tion     193 

Performance    specifications,    Corliss- 
engines 441-442 

Peterson  oil  filter,  operation 476 


PAGE 

Pickering  and  Gardner  governor 
catalogues,  selection  of 

throttling  governor 224 

PICKERING    GOVERNOR,    methods    of 

adjustment,  illustration.  ...    216 
safety   idler   feature,    illustra- 
tion     198 

Pipe,  velocity  of  fluid  in 449 

PIPING,  engine,  inspection 376 

indicator,  see  Indicator  piping ...      51 
steam,  simple  engine,  illustration  377 

PISTON,  clearance,  definition 3 

leakage,  rejection  losses  caused 

by 296 

low-friction,  illustration 302 

RING,  cast-iron  snap,  replace- 
ment   389 

expanding  by  peening 393 

fitting 390 

repairing,  illustrations 391 

replacement 389 

solid,  cutting 392 

tested  for  fit 393 

worn,  expanded  by  peening. . ;   393 
SLIDE    VALVE,    advantages    and 

disadvantages 88 

definition 27 

desirable  in  vertical  engines .      27 

inside  admission  type 88 

repair 394 

setting    for    selected    lead, 

illustration 121 

-rod   nuts,    methods   of  locking, 

illustration .    374 

PLANIMETER,  Amsler  polar,  operation     73 

averaging,  definition 74 

Coffin,  operation 75 

mean  effective  pressure  found  by     73 

polar,  adjustable  tracer  arm 74 

Willis 76 

Polar    planimeter,    adjustable    arm, 

diagram 74 

POPPET  VALVE 146-191 

advantages  and  disadvantages  159 
Ames   Unaflow  engine,   direc- 
tions for  setting 182-186 

definition 31 

detaching  or  releasing,  defini- 
tion       31 

ENGINE  efficiency  increased  by   146 

method  of  governing 195 

starting 385 

location  in  engine  cylinder. ...    160 

mechanism,  typical  designs 161 

operating      mechanism,      Vilter 

engine,  illustration .........    162 

positively-operated,  definition.  .      31 

reason  for  employing 146 

repair 395 

single-  and  double-beat,  defini- 
tion   160 

Portable  slide-valve  engine,  uses 323 

Porter  governor,  relation  between 
speed,  height  and  weights  of 
balls  and  counterpoise, 

formula 208 

Porter-Allen  engine,  variable-cut-off 
valve-mechanism,  illustra- 
tion   36 

POSITIVELY-OPERATED    CORLISS    and 

poppet  valves,  setting 173 

valve  mechanisms 149 

POWER,  definition 14 

HORSE    POWER,    see    also    Horse 

power. 

increase  due  to  condensing 
operation,  methods  of  cal- 
culating   285 


508 


INDEX 


PAGE 
POWER,  output,  generator,  formula.  .   354 

PLANT,  daily  load  curve 437 

drawing  from  "Power" iv 

efficiency    based    on    use    of 

rejected  heat 9 

inspection 373-377 

load  factor,  definition 438 

regular  inspection  trips  advis- 
able    387 

steam  engine,  formulas  for  com- 
puting       14 

stroke,  heat  engine,  definition. .  .      11 
"  POWER,"  energy  balance  in  electric- 
energy  distribution  circuits .   300 
hydrostatic   lubricator,  filled  by 

hand  oil  pump,  illustration . .  482 

oil  filter,  illustration 475 

power  plant  drawing  from iv 

savings  effected  by  superheating 

supply  steam,  table 423 

sight    feed    for    drop-feed    oiler, 

illustration 464 

valve  leakage  test,  single-valve 

engines 389 

valve  setting  without  removing 

chest  cover 132 

W.     H.     Wakeman     on     engine 

safety  devices 200 

"Power  House,"  hydrostatic  lubrica- 
tor, illustration 481 

PRESSURE  and  superheats,  maximum 

for  engine  valves,  table 421 

and    vacuum    gages    for    engine 

testing 344 

approximate      mean      effective, 

formula  for  computing 15 

average  or  mean  effective 12 

BACK,  definition 10 

purpose      of     reducing     with 

condenser 285 

boiler,  see  Boiler  pressure. 

effective,  on  piston 11 

indicator  springs,  table 53 

loss  indicated  by  steam  line 62 

MEAN       EFFECTIVE,        found       by 

method  of  ordinates 70 

in  cases  of  over-expansion ....     72 
indirect  methods  of  finding ...     77 

planimeter  for  finding 73 

net,  on  piston,  definition 10 

range  of  engine,  definition 258 

receiver,  see  Receiver  pressure. 

steam,  work  done  by 9 

PHONY-BRAKE    absorption    dynamo- 
meter, construction 347 

cooling 347 

illustration 347 

lubrication 348 

portable,      for      testing       small 

engines,  illustration 348 

Providence  Engineering  Corporation, 
jacketed     engine     cylinder, 

illustration 295 

Pulley,  governor,    method   of  secur- 
ing.     201 

Pumps,  inspection 375 

Q 

QUADRUPLE-EXPANSION  ENGINE,  com- 
bined indicator  diagrams.  . .   281 

definition 26 

seldom       used      in      stationary 

power  plants 280 

Quartered  main  bearing  illustration . .   396 


RACING,  causes 


222 


PAGE 

RACING,  definition 222 

engine     with     shaft     governor, 

causes 243 

RANKINE  CYCLE  ratios,  different  type 

engines,  table 309 

ratio,  definition,  formula 309 

standard     of     engine     perform- 
ance in  steam-engine  testing  304 

RANKINE  ideal  cycle 7 

water  rate,  formula 307 

Reach-rod,  Corliss  engine,  illustra- 
tion   383 

Re-babbitting,  necessary  where  bear- 
ings are  partially  melted  out  395 
RECEIVER-COMPOUND    ENGINE,     best 

receiver  pressure,  how  found  276 

definition 267 

RECEIVER  PRESSURE,  best,  receiver- 
er  compound  or  multi-expan- 
sion engine 276 

compound  engine,  dependent  on 

cylinder  ratio 278 

correct,   necessary  for   economi- 
cal operation   of   compound 

engines 276 

regulation  device,  illustration.  .  .    277 

variation  during  stroke 276 

Receiver  volume 269 

Reciprocating    engine    management, 

operation     and    repair.. 373— 415 
REDUCING  MECHANISM,  inclined-plane 

type,   illustration 49 

test   for  accuracy  of  reduction, 

illustration 50 

two   indicators    operated    from, 

illustration 57 

REDUCING  MOTION,  see  also  Indicator 
reducing  motion. 

indicator 43 

pendulum-level,  illustration 45 

REDUCING  WHEEL,  construction. .....     48 

principle,  illustration 48 

Regulation  guarantee  tests  for  gov- 
ernor   204 

Reheater,  definition 269 

Rejected  heat  in  steam  engine 6 

REJECTION  LOSSES,  cylinder  con- 
densation partly  responsible 

for 297 

definition 293 

exhaust    steam    used    for    heat- 
ing     297 

methods  of  decreasing 294 

Release  line,  purpose 67 

RELEASING  CORLISS-VALVE  MECHAN- 
ISM, definition 30 

illustration 152 

Releasing  mechanism,  operation 152 

Return  stroke,  definition .•  •  •  •      H 

Reversing  rocker,  reversing  rotational 

direction  of  engine 140 

REVOLUTION  COUNTER,  continuous. .  .    345 

definition 344 

hand 344 

Reynolds  trip  gear 155 

Rheostat,    water,    generator   loading 

accomplished  by 357 

Rice  and  Sargent  Corliss  engine, 
jacketed  cylinder,  illustra- 
tion   295 

Rice-Stix  Dry  Goods  Company  plant, 

engine  indicator  diagram . . .  329 
RICHARDSON-PHENIX    COMPANY, 
crosshead-pin  telescopic 

oiler,  illustration 472 

oil  filter,  illustration 476 

sight-feed  oiler  for  gravity  sys- 
tem, illustration 468 


INDEX 


509 


PAGE 
RIDGWAY    automatic    engine,    Rites 

governor,  illustration 247 

FOUR-VALVE  ENGINE,   valve  set- 
ting directions 178 

valve-operating  mechanism, 

illustration 148 

SIMPLE  and  cross-compound  four- 
valve  engines,  results  of 

adjustments,  table 179 

four-valve     engine,     table     of 

dimensions  for  setting 179 

tandem  compound  four-valve 
engine,  results  of  adjust- 
ments, table 181 

Ridgway   Engine   Company,    recom- 
mendation for  valve  setting 

for  unequal  leads 130 

RIDING-CUT-OFF    VALVE,    advantages 

and  disadvantages 91 

definition 27 

engines  with,  uses. 324 

mechanism,  setting,  explana- 
tion  ... 133 

Right-hand  engine,  definition 21 

RiNG-oiled  bearing  illustration 465 

packing,  soft,  illustration 404 

snap,  piston,  repairing,  illustra- 
tions   391 

RITES  GOVERNOR,   dash-pot  or  drag 
springs  for  limiting   rate  of 

movement 246 

illustration 232 

ridgway     automatic     engine, 

illustration 247 

special  adjustments 248 

ROBB-ARMSTRONG  SWEET  GOVERNOR, 

adjustment 249 

description 248 

Robertson,  James  L.  and  Sons,  Willis 

planimeter,  illustration 75 

Rod  area,  effect  in  computing  work 

done 13 

ROPE    BRAKE    absorption    dynamo- 
meter   350 

illustration 351 

ROTARY  STEAM  ENGINE,  construction 

and  disadvantages 319 

illustration  of  principle 320 

operation 320 

ROTATION,  slide-valve  engine,  rever- 
sing direction  of, 140 

method,    tare-weight    of    brake 

found  by 349 


St.  Louis  Iron  and  Machine  Works, 
piston  construction  in  St. 
Louis  Corliss  engine,  illustra- 
tion   374 

SAFETY  idlers,  belt-driven  governors.    198 
knock-off     cams,     Corliss     gov- 
ernors      198 

stop,   engine  governor  provided 

with 198 

Saturated    steam    and    superheated 

steam,  differences 418 

Saybolt  viscosimeter,  illustration 454 

Schaeffer  and  Budenburg  Manufac- 
turing Company  fixed  tacho- 
meter, illustration 346 

Schutte  and  Koerting  Company, 
catalogue,  Corliss  engine 
with  condenser,  illustration,  284 

Scotch-yoke  mechanism  velocity  dia- 
gram   102 


PAGE 

Selected  equal  leads,  definition 114 

SETTING,  dimensions  for,  Ridgway 
simple  four- valve  engine, 

table 179 

plain  slide  valves  for  equal  leads, 

table  showing  procedure  11&-118 
slide  valve,  first  consideration. . .    113 

steam-engine  valves 107 

SHAFT    governed     engine,     eccentric 

shifting  inadvisable 115 

governing,  forces  required 229 

GOVERNOR,  adjustment 245 

balance 235 

care  of... 245 

classification 236 

classification  table 240 

crank    pin    used    in    place    of 

eccentric 239 

definition .    37,  228 

full-load   running    position, 

illustration 141 

hammering,  remedy 246 

methods  of  adjustment 229 

method  of  controlling  engine 

speed 233 

methods  of  controlling  engine 

valves 239 

more  economical  than  throt- 
tling governor 228 

OPERATION,    effects    of  weight 

and  spring  adjustment ...    241 
forces    of     two    kinds    em- 
ployed     229 

troubles  and  remedies . .    243-245 
permanent  control,  effected  by 

centrifugal  force 230 

position  fixed 256 

principal  adjustments,  table.  .    242 
PRINCIPLES  and  terms  same  as 

those  for  fly-ball  governor  229 

and  adjustments. 228-257 

results    of    combining    centri- 
fugal force  and  inertia 232 

simple  weight  employed,  illus- 
tration     238 

sluggishness,  causes 243 

speed  regulation  and  govern- 
ing action 233 

temporary  control  effected  by 

inertia 231 

type  of  engine  used  on 228 

use  of  both  centrifugal  force 

and  inertia,  explanation 233 

variable  cut-off  governor 228 

"Shaft  Governors,"  Hubert  E.  Col- 
lins on  shaft  governor  opera- 
tion   239 

Sherwood  Manufacturing  Company, 
oil  collecting  devices,  illus- 
tration   472 

Shims,  bearings  adjusted  by  means 

of 400 

Short-stroke  engine,  definition 32 

Side-crank  engine,  definition 20 

Sight-feed  oiler,  four  window,  gravity 

oiling  system,  illustration . . .   468 
SIMPLE   balanced-slide-valve   engine, 

illustration 321 

D-slide  valve  engine,  illustration     23 

SiNGLE-acting  engine,  definition 11 

-beat  poppet  valve,  definition. . .    160 

-ECCENTRIC  DETACHING  CORLISS- 

VALVE  engine,  valve  setting 

directions 163-169 

mechanism,  features 154 

-VALVE  ENGINE,  definition 32 

simple,  construction  and  opera- 
:    ,          tion 321-323 


510 


INDEX 


PAGE 

SKINNER    engine-governing    mechan- 
ism, illustration 228 

tandem-compound   engine,   gov- 
erning      of       high-pressure 

cylinder,  illustration 259 

"  UNIVERSAL  UNAFLOW"  ENGINE, 

steam-consumption  curves  331 
valve-operating  mechanisms, 

illustration 161 

SLIDE  VALVE,  see  also  Valve,  slide.  84-144 

balanced,  illustration 89 

condensing  engine,  starting 380 

definition 26 

displacement,  definition 101 

engine,  direction  of  rotation 140 

function 84 

iNsiDE-admission,  illustration ...      87 

clearance,  definition 95 

lap,  how  changed 96 

mechanism  adjustment Ill 

method     of     controlling     steam 

flow 84 

motion  received  from  eccentric .  .      97 
multiported,      advantages      and 

disadvantages 90 

outside-admission,  illustration.  .      87 
plain,  setting  for  selected  lead, 

illustration 123 

proper  lead 115 

riding-cut-off,     advantages    and 

disadvantages 91 

SETTING,  defects  determined  by 

indicator 143-144 

effect  of  governors  on 140 

first  step 113 

FOR    EQUAL  CUfc-offs 129 

.leads 115 

without  removing  steam  chest 

•    cover,  explanation 132 

three  conditions  to  be  set  for.  .  113 

type  of  engine  used  in 84 

Snap  ring,  fitting,  illustration 390 

Sounding  rod,  knocks  located  by 412 

"Southern    Engineer    Kink    Book," 

engine  alignment 408 

"SOUTHERN    ENGINEER,"    oil    filter, 

illustration 474 

riding-cut-off  valve  setting . .    134-140 
SPEED,     governor     adjustments     for 

changing 212 

method     of     control     by     shaft 

governor 233 

regulation,  good  shaft  governor . .  233 

VARIATION,  fly-ball  governor. .  . .  195 
governed      and      ungoverned 

engines,  graph 193 

SPLASH  oiling  systems,  advantages .  .  .  470 
-oiled  engines,  table  of  oils  for . . .  460 
system,  external  bearing  lubrica- 
tion   465 

SPRING    adjustment,    shaft-governor 

operation,  effects. 241 

INDICATOR,  see  Indicator  springs. 

adjustment 56 

classification 52 

rules  for  selection 55 

safe  pressures,  table 53 

testing  apparatus,  illustration .  54 
-LOADED    governor,    advantages 
over  simple  pendulum  gov- 
ernor   207 

governor,      comparison      with 

weight-loaded 209 

STANDARD  CRANK-MECHANISM,  defini- 
tion   34 

velocity  diagram 102 

STARTING      block,      Corliss      engine 

governor 385 


PAGE 
STARTING  block,  lever  and  wrist  plate, 

Corliss  engine 384 

STEAM  and  feed-water  cycle  in  power 

plant,  illustration 306 

chest  diagram,  value 64 

CONSUMPTION,         CALCULATION 

from  indicator  diagram. .  .      80 

on  dry-steam  basis 304 

condensing  and  non-condens- 
ing engines,  table 286 

uniflow  engine,  variation  in. . .   294 

dry,  weight  of 304 

ENGINE,  see  also   Engine,  steam. 
approximate  attendance  costs, 

graph 439 

condensing  and  non-condens- 
ing, stopping 382 

condensing    operation,   defini- 
tion      283 

conditions  necessary  for  high- 
est theoretical  efficiency.  ...        6 
costs  of  different  types,  table .  .    340 

depreciation  rates 431 

EFFICIENCIES     and     perform- 
ance, tables 311-317 

how  increased 291-317 

mathematical     methods     of 

computing 302-317 

ways  of  expressing 303 

efficient,  definition 9 

ELEMENTARY,  construction. ...       2 

operation 3 

energy  abstracted  from  steam .        7 

expansion  line  in 65 

first  cost,  factors  influencing.  .   335 
fly-ball    governors,    principles 

and  adjustment 192-227 

function  and  principle 1-18 

GOVERNOR,   see   also  Governor, 
steam-engine. 

functions 37 

heat  converted  into  mechan- 
ical work 291 

horizontal,  definition 20 

inclined,  definition 20 

ideal,  illustration 7 

indicators 40-83 

LOSSES,  classification 293 

large  part  unavoidable 292 

LUBRICATION 447-487 

selection  of  oils  for,  tables. . . 

456-460 

systems,  classification 460 

mechanisms     and     nomencla- 
ture     19-38 

MODERN,    classification    as    to 

type,  table 336-339 

types 319-340 

packings  for 403 

performance  guarantees 440 

plant,  heat-flow,  explanation. .        1 
power,  formulas  for  computing     14 

purposes  of  testing 342 

rejection    losses,    methods    of 

decreasing 294 

rotary,   construction  and  dis- 
advantages     319 

specifications  for  quotations..   444 
suitable  applications  for  drop- 
feed  lubrication 462 

TESTING,  see  also  Engine  test- 
ing     342-372 

data  and  results 369-371 

ideal  Rankine  cycle  stand- 
ard of  engine  performance  304 

TYPE  using  slide  valves 84 

classification  table 19 

VALVES,  repair 393 


INDEX 


511 


PAGE 

STEAM  ENGINE  VALVE,  setting 107 

vertical,  definition 20 

warmed    and    drained    before 

starting 377 

water  rate  taken  as  measure  of 

economy 308 

"  Steam  Engine  Test  Code,"  American 
Society  of  Mechanical  Engi- 
neers, Outline 369-371 

"STEAM  ENGINE  TROUBLES,"  H 
HAMKEN  ,  enclosed-spring 

governor,  illustration 202 

governors 193 

governor  with  horizontal  ten- 
sion spring,  illustration 194 

STEAM  expansion  line,  form  of  curve .  .      16 

EXPANSIVE  USE,  economy 12 

when  not  desirable 13 

FLOW,  controlled  by  slide  valve  84-87 

DIRECTION,    INTO    COUnterfloW- 

engine    cylinder,    illustra- 
tion       33 

uniflow-engine     cylinder, 

illustration 33 

jacketing,  method  of  decreasing 

rejection  losses 296 

LINE,  ideal 63 

pressure  losses  indicated  by. . .      62 

variations,  illustration 63 

methods     for     controlling    used, 

with  fly-ball  governors 195 

port     locations,      marking     for 

valve  setting 127 

"Steam  Power,"  Hirshfeld  and 
Ulbricht,  engine  classifica- 
tion   19 

"STEAM  POWER  PLANT  ENGINEER- 
ING," frictional  losses  of 

engines 301 

Gebhardt,  steam  engine  efficien- 
cies       and         performance, 

tables 311-317 

STEAM  quality  determination 362 

rate,  four-valve  engines 327-329 

saturated  and  superheated,  dif- 
ferences    418 

SUPERHEATED,    see    also    Super- 
heated steam. 

use  in  engines 417-426 

TOTAL,  used  per  hour  by  engine . .     81 

work g 

WEIGHT  USED  by  engine  with  no 

clearance,  formula 79 

computation 78-81 

WORK  DONE  BY  direct  pressure '.  9 

expansion 12 

work   necessary   to   expell   from 

cylinder 4      IQ 

Stone,  A.  O.,  hydrostatic  lubricator, 

illustration 481 

STROKE,  definition 11 

working,     heat     engine,     defini- 
tion       11 

Stuffing  boxes,  inspection 375 

SUPERHEAT,    effect  of,  B  u  c  k  e  y  e 

engines,  graph 423 

influence  on  water-rate,  graph . .  .    423 
and     pressure,     maximum     for 

engine  valves,  table 421 

SUPERHEATED  STEAM,  advantages  and 

disadvantages,  table 425 

and     saturated     steam,     differ- 

..  ences    418 

cylinder  oil  for  engines  using.  .  . .   421 
desirability      of      compounding 

partially  obviated  by 422 

economical  in  uniflow  engines.  ..   424 


PAGE 

SUPERHEATED    STEAM,   effect    in    de- 
creasing cylinder  condensa- 
tion   and    leakage,    graph..  425 
gain     resulting     from     use     in 

engines 417 

generation 418 

metals     for     valves     and     seats 

used  with 421 

USE     IN     compound     or    triple- 
expansion  engines 424 

engines 417-426 

valves  for  engines  using 419 

Superheater  installation,  typical,  illus- 
tration     418 

SUPERHEATING,  effect  on  efficiency  of 

simple  engine,  graph. '. 295 

supply  steam,  saving  effected  by, 

table 423 

Supplies,  engine,  inspection 377 

SWEET  governor,   operating  gridiron 

valve,  illustration 244 

valve,    Erie    Ball    Engine    Com- 
pany, illustration 90 

Symbols  list xii 


Tabor  indicator,  curved-slot  parallel 

motion,  illustration 44 

TACHOMETER,    definition 345 

fixed 346 

hand 346 

TANDEM-COMPOUND  ENGINE  com- 
bined diagrams 272 

definition 23 

governing      of      high       pressure 

cylinder,  illustration 259 

starting 387 

surface      condenser      connected 

with,  illustrati9n 284 

typical  high-speed,  illustration.  .    323 
water  rate  determination,   illus- 
tration     366 

Tare-weight  of  brake,  definition 348 

Telescopic     tubes,     eccentrics     and 

crosshead  pins  oiled  by 473 

Temperature  range  of  engine,  defini- 
tion   258 

TEMPLET,  application  in  finding  dead 

centers  of  eccentric 106 

arrangement  on  valve  chest  for 

valve  setting,  illustration.  ..    128 
method    of    ascertaining    valve 

operation 109-111 

valve  setting,  for  indirect-valve 

engine 126 

Terminal    drop,    compound    engine, 

definition 271 

"Test     Code,"     American     Society 
of     Mechanical     Engineers, 
water-rate  test  specifications  365 
Testing,     engine,     see    also    Engine 

testing 342-372 

Test  results  facilitated  by  calculation 
of  engine  and  brake  con- 
stants   368 

Theoretical  water  rate  computation, 
based  on  ideal  Rankine 

cycle  formula 307 

THERMAL  EFFICIENCY  based  on  brake 

horse  power,  formula 310 

computation      on      basis      of 
indicated      horse    power, 

formula 307 

definition 303 

computation 364 

formula 305 

test,  purpose 342 


512 


INDEX 


PAGE 
THERMAL  LOSS  cylinder  condensation 

partly  responsible  for 297 

definition 8,  293 

method  of  reducing 299 

Thompson  indicator,  illustration..   40,  42 
THOMSEN,    T.    C.,    lubrication   chart 
for     steam     cylinders     and 

valves 457 

"Practice  of  Lubrication,"  selec- 
tion of  oils  for  engine  lubri- 
cation, tables 456-460 

Throttling  governor,  selec^n 224 

Thurston,  T.  G.,  Gravity-circulation 

system,  illustration 469 

Tolle  governor,  general  arrangement, 

illustration 209 

Tools,  engine,  inspection 377 

TORQUE,  definition  of  term 260 

regularity  increased  in  compound 

engines  explanation 265 

variation  graphs,  tandem-com- 
pound engine 266 

Tram,  illustration 104 

TRAMMEL,  application  in  finding  dead 

centers  of  eccentric 107 

gage,  valve  setting  with 125 

method    of    placing    engine    on 

dead  center 104 

Travel,  valve,  definition 98 

Trinks,    W.,     "Governors    and    the 
Governing          of         Prime 

Movers"  on  racing 222 

TRIP  GEAR,  function 157 

operation 152 

Reynolds,    for    Corliss    engines, 

illustration 152 

TRiPLE-compound  engine,  definition.      25 
EXPANSION  ENGINE,  definition. .  .      25 
seldom     used     in     stationary 

power  plants 280 

use  of  superheated  steam 424 

pumping,    receiver    and  drain 

arrangement,  illustration. .  .   270 
TROT  AUTOMATIC  ENGINE  directions 

for  reversing 235 

method    of    balancing    governor 

flywheel,  illustration 236 

Troy  Engine  Company  method  for 
setting    vertical    engine    on 

dead  center 105 

Trunk-piston  mechanism,  definition.     35 
Twin-cylinder  engine,  definition 23 


U 


UNIFLOW  ENGINE,  construction  and 

operation 33J 

CYLINDER,     connection    to    sur-  *** 

face    condenser,   illustration  283 
direction  of  steam  flow  from, 

illustration '    34 

lubrication 424 

definition 33 

four-valve,    for    non-condensing 

service 329 

manufacturer's  guarantees 443 

most     profitable     degree     of 

vacuum 289 

NON-CONDENSING,     construction 

and  operation 332 

economy 333 

starting 385 

superheated  steam  economical  424 
"Universal  una-flow"  engine,  valve- 
operating  mechanism,  illus- 
tration     161 


PAGE 


VACUUM,  actual  and  theoretical  dif- 
ference    382 

most  profitable  degree  in  uniflow 

engine 289 

Oil    Company,    cylinder    oil    for 

use  with  superheated  steam .    422 
VALVE    adjustments,    importance    of 

dead  centers 103 

arms,  steam  and  exhaust,  Harris- 
burg  four-valve  engine,  table 

showing  advance 178 

automatic  by-pass,  Ames  una- 
flow  engine,  illustration 185 

balanced  slide,   advantages  and 

disadvantages 89 

CHEST,  templets  arranged  on.  ...    129 
vertical-engine,    measurement 

for  valve  setting 127 

Corliss,  see  also  Corliss  valves  146-191 
D-SLIDE,    advantages    and    dis- 
advantages       87 

illustration 26 

detaching-poppet  admission, 
"Hamilton"  engine,  illus- 
tration   32 

diagrams,  definition 84 

double-ported  Corliss,  illustra- 
tion   29 

ellipse,  definition 84 

ENGINE,  repair 393 

using        highly       superheated 

steam 419 

friction  in  engines 301 

GEAR  ADJUSTMENTS,  Ames  una- 
flow  engines,  table  showing 

effects 187 

effects    on    detaching    Corliss- 
valve  engines,  table 170-171 

Allis-Chalme.rs      heavy      duty 

Corliss  engine,  illustration. .    158 
Ames  four-valve  non-releasing 

Corliss  engine,  illustration.  .    150 
"Valve  Gears,"  C.  H.  Tessenden,  on 

valve  diagrams 84 

VALVE,  governor-operated  cut-off.  ...      28 

gridiron,  illustration 28 

HAND-adjustable  cut-off 28 

-operated,   engine   with,   illus- 
tration          4 

inspection 374 

LAP,  definition 94 

effects  of  changing,  table 96 

LEAKAGE,  rejection  losses  caused 

by 296 

revealed  by  expansion  line.  ...      66 
single  valve  engine,  test  for .  .  .   389 
maximum  pressures  and  super- 
heats   for    different    types, 

table 421 

MECHANISM,  releasing  or  detach- 
ing, definition 30 

variable-cut-off,  engine  equip- 
ped with,  illustration 36 

Meyer  riding-cut-off,  illustra- 
tion   28 

multiported  slide,  illustration.  .  .      27 
operating  mechanism,  Mclntosh 
and  Seymour  engine,  illus- 
tration       92 

OPERATION,  indirect-measure- 
ment method  of  ascertain- 
ing   108 

Ridgway     four-valve     engine, 

illustration 148 

PISTON    SLIDE,    advantages    and 

disadvantages 88 


INDEX 


513 


PAGE 
VALVE,  PISTON  SLIDE  comparison  to 

D-valve 27 

POPPET,  see  also  Poppet  valves  146-191 
single-seated  admission,  illus- 
tration       31 

positively-operated    poppet    ad- 
mission, illustration 31 

SETTING,  Ball  Corliss  engines .  .  .  .    173 
Chuse      condensing      uniflow 

engine 188 

compound  engine 280 

Corliss  and  Poppet  valves.  146-191 

defects,  remedies 143-144 

double-eccentric         detaching 

Corliss- valve  engines 172 

"  Fleming-Harrisburg  "      four- 
valve  engine 175-178 

Lentz  poppet-valve  engines  188—190 

measuring  rod  for 126 

methods  of 107 

new  engine 112 

old  engine 113 

operations,  indicator  used 142 

Ridgway  four-valve  engine...    178 
selected  equal  leads,  example, 

illustrations 119 

shaft-governed  engine 114 

single-eccentric    detaching- 
Corliss-valve  engine 163-169 

templets  used  for 129 

unequal  leads 130 

Vilter  poppet-valve  engine. .  .  .    190 

with  trammel  gage 125 

without  removing  chest  covers, 

example 125 

simple   automatic,   engine   with, 

illustration 4 

single-ported  Corliss,  illustration     28 

SLIDE,  see  also  Slide  valve 84-144 

flat  type 26 

piston  type 26 

stem  adjustment,  illustration 111 

TEMPLET,  laying  off 127 

length 128 

TRAVEL   with   eccentric    motion, 

illustration 98 

relation  to  eccentricity 99 

VARiABLE-cut-pff  engine,  definition.  .      37 

speed  engine,  definition 216 

Velocity  diagram,  standard  crank  and 

scotch-yoke   mechanisms...   102 

Vertical  steam  engine,  definition 20 

VILTER  MANUFACTURING  COMPANY, 
Corliss-valve  trip  gear,  illus- 
tration   156 

poppet-valve     engine,     illustra- 
tion     160 

Tolle  governor,  illustration 209 

Watt     governor     number     two, 

illustration 214 

Vilter    poppet-valve    engine,     valve 

setting  directions 190 

Viscosimeter,  illustration 454 

VISCOSITY     OF     liquid,     definition  . .  450 
oil,  variation  with  temperature 

change 450 

Voltmeter,  use  in  determining  output 

of  generator 354 

W 
WAKEMAN,  W.  H.,  in  "Power"   on 

engine     safety     devices ....  200 


PAGE 
WATER  BRAKE,  horse  power  absorbed 

by. 352 

definition  and  operation 352 

principle,  illustration 352 

WATER  in  cylinder,  knocks  caused  by  410 
RATE,    approximate    calculation 

by  means  of  indicator  cards .   364 
calculation   on   basis   of  indi- 
cated horse  power,  formula .   363 
determination    by    boiler-feed 

method 361 

STEAM  ENGINE,  determination 

by  steam  condenser. . . .   357 

measure  of  economy 308 

tandem-compound  engine, 

equipment  for  determining.   366 
TEST,  apparatus,  illustration..   358 

data  sheet 362 

purpose 342 

simple  engine 360 

wet  steam  weight  expressed 
in    terms    of    dry    steam 

weight 336 

American    Society    of 
Mechanical  Engineers' 

specifications 365 

theoretical,  computation  based 
on  ideal  Rankine  cycle,  for- 
mula    307 

rheostat,  explanation,  illustra- 
tion   357 

Watt,  James,  inventor  of  governor. . .    193 
Wattmeter,  direct-current,  load-put- 
put  of  generator  determined 

with 355 

WATT'S  governor,  illustration 193 

high-speed  loaded  governor,  gen- 
eral arrangement,  illustra- 
tion   214 

indicator,  operation 41 

Wear,  definition 447 

WEIGHT  adjustment,  shaft-governor 

operation,  effects 241 

-LOADED  GOVERNOR,  advantages 
over  simple  pendulum  gov- 
ernor   207 

comparison      with      sp  r  i  n  g  - 

loaded 209 

Weiss,  W.  R.,  hydrostatic  lubricator 
filled    by    hand    oil    pump, 

illustration 482 

Wheel,  reducing,  use  of 48 

Wiley,   John  and   Sons,   engine  per- 
formance tables 311-317 

Willis  planimeter,  illustration.  '. 75 

WIPER  CUP,  eccentrics  and  crosshead 

pins  oiled  by 473 

method  of  using  in  oiling  cross- 
head  pin,  illustration 472 

WoOLF-compound  engine,  definition, 

illustration 267 

-tandem  compound  engine,  tem- 
peratures in  various  parts, 

illustration 263 

WORK,  net,  steam  upon  piston 11 

per  double  stroke  by  any  engine, 

formula 13 

total,  done  by  steam 8 

Wrist-pin  bearing,  heating 403 


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